To have your most-used apps open automatically whenever you log in, open System Preferences and click on Accounts. Click Login Items and then the plus sign (+) button. Navigate to the item you want to launch and click Add. (Or add items by dragging them from the Finder to the Login Items list.) This works for documents and websites too.

To add a site to the list, first drag its icon from the browser’s address field to the desktop. Then drag the resulting .webloc file to the Login Items window. To remove an item from the list, select it and click the minus (-) button.