Last week I showed you how to connect your Mac to the Internet and to a local network. Now that your computer is on speaking terms with other devices and services, let's examine exactly how you can put those powers of communication to use for sharing the devices and files associated with your Mac.

Sharing options for nearly everyone

To share elements of your computer with others, you must first grant permission for certain kinds of sharing to take place. You do this via the Sharing system preference, which you'll find in the Internet & Wireless section of Mountain Lion's System Preferences window. Once you've selected Sharing, you'll see a number of options. We'll start by looking at the ones you'll use most frequently.

Screen Sharing: This feature lets you remotely view the screen of another Mac on your local network, as well as optionally control that Mac. It has been part of the Mac OS for quite some time, and with Mountain Lion it's dead simple to use.

To allow someone to share your screen, you must first make the option available. To do that, open the Sharing preference and enable the Screen Sharing option. Once you've enabled Screen Sharing, you can designate exactly who may exercise this privilege.

By default, only people who have an Administrator's account can share your screen. You can also allow specific users or groups from your list of contacts to screen-share with you. To do this, confirm that the Only these users option is selected, click the plus (+) button, choose Contacts or groups in the contacts sheet that appears, and click Select. This action will add them to the list of users who can request screen-sharing access. If you enable the All Users option instead, anyone who can see your computer on the local network can share your screen.

To share your screen, all that someone on your network need do is select your Mac under the Shared heading in a Finder window's sidebar and then click the Share Screen button that appears near the top-right of that window. The person will be prompted to provide an approved username and password for the shared Mac. Alternatively, the would-be sharer can enter the Apple ID associated with that Mac. Simply clicking Connect completes the connection. We'll discuss the ins and outs of screen sharing in another column.

File Sharing: If you enable File Sharing, others on your network can, well...share files with you. Setting up this arrangement doesn't entail granting them complete access to your Mac. Rather, it allows them to copy files from their Mac into folders on your computer that were created specifically for sharing. By default, one such folder exists for precisely this purpose. It's called the Drop Box folder and you can find it by following this path: youruserfolder/Public/Drop Box. Each user account has such a Drop Box folder.

The Drop Box folder earns this name by providing a folder destination that others can copy files to, but without being able to see other files that it may contain. Think of it as being akin to the company Suggestion Box--the padlocked one that has a slot in the top for inserting notes that complain about Margie in Accounting. You can place all the disparaging notes you like in that box, but only the person with the key can view them.

In order for people to copy items into your account's Drop Box, they must first select your Mac from a Finder window's sidebar. The word 'Connecting' will appear at the top-left of the window, and within that window will appear the names of all user accounts on that Mac, followed by 'Public Folder'. So, for example, 'Chris' Public Folder'. Double-click this folder, and you'll find the Drop Box folder within. If you try to open the Drop Box folder, your Mac will inform you that you can't pry it open because you don't have permission to. However, you can drop things into it, at which point they'll be copied to the Mac that hosts the folder.

You can create other folders on your Mac for sharing. To do so, move to the Finder and choose File > New Folder (Shift-Command-N) to create a new folder on the desktop in the window that appears. Select that folder, choose File > Get Info (Command-I), and enable the Shared Folder option. This folder will appear as a shared folder from another Mac on the network.

Simply designating the folder as shared doesn't complete the picture, however. You must also decide what kind of access others should have to the folder.

At the bottom of the Info window that remains open, click the triangle that appears next to Sharing & Permissions. You'll see three listings: your username, 'Staff', and 'Everyone'. Next to your user name will be the words 'Read & Write'. 'Read only' appears next to 'Staff' and 'Everyone'.

With the settings in this configuration, people on other computers can see what's in the folder and can copy items from it to their Macs. They can't, however, add files to the folder. You might set up a folder with these characteristics as a "come-and-get-it" folder where family members or coworkers can go to pick up specific files, without being able to fill the folder with their own stuff. You can change that folder behavior easily enough, if you wish to.

Click the Read Only entry next to Everyone, and you'll see four options: Read & Write, Read Only, Write Only (Drop Box), and No Access. Read & Write permits anyone with such access to take items out of the folder and to put items into it. I've already explained what Read Only does. Write Only describes the behavior of a Drop Box folder: A networked user can place items in it, but can't otherwise access the folder's contents. And No Access means that others don't have permission to access the folder in any way.

Why does Apple include a No Access option? Within this same area, you can add other users. Some you may wish to grant access to, while others you may want to keep strictly out. If you're afraid that Margie's feelings may be hurt by comments regarding her work ethic, assign her No Access privileges for that folder.

Printer Sharing: At one time, if you wanted to share a printer with other computers on your network, you had to purchase a model that sported an ethernet jack and then incorporate the thing into a wired network. Those days are long gone--and not only because many printers today support Wi-Fi. You can share printers that have no wireless capabilities whatsoever. And the way you do it is with the Printer Sharing option.

Simply connect your printer to your Mac in the usual way (that's most often via a USB cable), enable Printer Sharing in the Sharing preference, and choose which printers you want to share across the network. (You may have just one or more than one.) The printer you select will appear as an option for any Mac on your network. (You can also choose to share a printer from within the Print & Scan preference.)

Scanner Sharing: See "Printer Sharing." Same idea.

Advanced sharing options

We now venture into options intended for advanced users. Rather than confuse you with a lot of technical terms and convoluted explanations, I'll lay out the gist of what the remainder of the sharing options do.

Remote Login: This sharing option allows you or other people to gain remote access to your computer's files. To do so, they use something called the Secured Shell (or SSH) scheme. This scheme requires that the person attempting to log in know the username for the account you wish to access, the account's password, and the computer's IP address. (I discussed IP addresses when I discussed setting up your network.) As with File Sharing, you can choose to allow anyone in who has this information, or you can restrict access to individual users that you specify.

The advantage of remote login is not only that it lets others on your network gain access to your files, but also, through a bit of configuration magic that I won't go into now, that it lets people on the Internet outside your local network do so. Unless you know what Remote Login is for and have a specific need to enable it, leave it unchecked.

Remote Management: I've already discussed the Screen Sharing option. Remote Management is quite similar: It allows people on your network or across the Internet to view and control your Mac remotely while connected to your computer via a VNC (Virtual Network Computing) client. Again, you must choose who can have access to your Mac. And also again, if you don't understand or need this capability, leave it off.

Remote Apple Events: Built into the Mac are tools for automating tasks on your computer. Many such tasks are created with and executed by something called AppleScript. When you enable this sharing preference, you're telling your Mac to accept actions (or "Apple Events") sent from another computer on the network. For example, an Apple Event might tell your Mac to print all the documents within a particular folder on your desktop. As before, you can choose who you grant this power to. And yes, leave it off if you don't understand or need it.

Internet Sharing: Suppose you're in a hotel that offers a wired Internet connection rather than Wi-Fi. You can plug your MacBook Pro into this connection to get on the Internet, but what about your Wi-Fi iPad? If only you could somehow share the Mac's connection...

You can, and Internet Sharing is the way. In our scenario, choose Ethernet from the 'Share your connection from' pop-up menu, and select Wi-Fi in the 'To computers using' list. Or in English, "Hey, my Mac's connected to the Internet via an ethernet cable. You're welcome to share that connection with your iPad over Wi-Fi."

When you switch on Internet Sharing, you'll be asked if you really want to do this (of course you do). Click Start. The Wi-Fi icon in the menu bar will turn gray and display a white upward-pointing arrow, indicating that it's sharing its Internet connection. On the device you wish to use to glom onto that connection, open its Wi-Fi settings and choose your Mac as the hotspot.

If you don't want everyone and her brother sharing this connection, click the Wi-Fi Options button at the bottom of the Sharing window before you enable Internet Sharing. In the sheet that appears, you can name the network, choose a channel (you're safe leaving it at 11), and select the kind of security that you wish to use ('None' or 'WPA2 Personal'). If you choose to use security, you'll have to enter and confirm a password for your network.

Bluetooth Sharing: Bluetooth is a short-range networking scheme that lets you do things such as broadcast music from your iPhone to a set of wireless headphones or to a car's audio system. Wireless mice, trackpads, and keyboards also use Bluetooth to send their signals to your computer.

You can also share files over Bluetooth, a capability that can come in handy if you have a couple of Macs that you can't network in another way (because there's no Wi-Fi available, for example). This is how to do it.

First, enable Bluetooth Sharing. Once you've done so, you have some decisions to make. One is to figure out how to handle an item that you receive as a Bluetooth transfer. You can automatically accept and save it, automatically accept and open it, receive a prompt to manually accept or decline it, or never allow such transfers. You then select a folder where you'd like transferred items to appear (Downloads is the destination by default).

Another user can also browse your computer over Bluetooth. In the next section of the window, you may choose  to allow this browsing automatically or to be presented with a dialog box where you can make such decisions case by case. In the same section of the window, you also select the folder that the connected user can browse. (By default, this is the Public folder within your user folder, but you can select a different one.)

To establish a connection over Bluetooth, each party must have Bluetooth switched on and discoverable. (Both options are located in the Bluetooth system preference.) To make a connection, click on the plus (+) button at the bottom of the Bluetooth window. Bluetooth Setup Assistant will launch, and the names of any discoverable devices will appear in its window. Select the one you wish to connect with, and click Continue.

Bluetooth Setup Assistant will generate a code on the Mac where it's currently running and will send that code to the device that you wish to connect to. The other device must acknowledge that code. Once it does, the two devices are paired. Quit Bluetooth Setup Assistant, and you'll find your paired device listed in the Bluetooth system preference.

To send a file to a paired device, click the Bluetooth menu in the menu bar, locate the name of the paired device, and choose Send File from the device's submenu. In the window that opens, you can navigate to the item you wish to send. Select the item and click the Send button in the window. An Incoming File Transfer window will appear on the other Mac by default. Click Accept on that Mac, and the system will transfer the file to the folder configured to accept it.

You can browse another device similarly. Click the Bluetooth menu, but this time choose the paired device and select Browse. You can then see the contents of the folder that the other user has granted you access to.

Note that you can't use Bluetooth to share files between iOS devices. Although the iPod touch, the iPhone, and the iPad have Bluetooth capabilities, they don't support file transfer.

The last thing: AirDrop

If this last operation sounds especially tedious, I have good news for anyone who uses Lion or Mountain Lion and wishes to quickly transfer items from one Mac to another. That good news is called AirDrop, and it works like this.

With each Mac connected to Wi-Fi, open a Finder window on both computers. Select AirDrop in each window's sidebar. Any Macs that are running Lion or Mountain Lion on your local network and that have their AirDrop window open will appear as round icons in the window, with their names below. To transfer a file from your Mac to another Mac, simply drag the file on top of the other computer's icon. You'll be asked if you'd like to send that file. Click Send, and a notification will appear on the other Mac, inviting you to save and open, to decline, or to save. Click Save and Open or Save, and the item will be transferred to the other Mac and placed in that Mac's Downloads folder.

If that Mac can open the file, and you've chosen 'Save and Open', it will do so in the appropriate application. If the Mac lacks the necessary application to open the file, but the Mac is aware of which application created it (and that application is available from the Mac App Store), a notification will warn you that you're missing the application, but that you can get it from the Mac App Store. Tell your Mac to get it, and the Mac App Store application will open and direct you to the application. You can then choose to purchase it.

Next week: Users & Groups

See also:

Microsoft joins list of recently hacked companies

10 top creative tools and apps for the iPad

Apple's musical revolution

Why the iPad still can't be a true Mac replacement

How to stay connected after disaster strikes