iCloud can be a ray of sunshine for iOS device owners looking to keep their documents synced between multiple devices and computers. Apple's own iWork suite, unsurprisingly, already offers deep iCloud integration for keeping your Pages, Numbers, and Keynote documents in sync between devices. At this writing, however, only Apple's iOS iWork apps support iCloud; it's not yet possible to sync your documents directly with the Mac versions of the apps unless you use workarounds.
But iCloud document syncing--a concept Apple refers to as Documents in the Cloud--works great between the iPad, iPhone, and iPod touch. The process is very similar in all three iWork apps; let's use Pages as our example.
If it's your first time launching Pages, or your first time launching the app after updating to its latest version, you may see a prompt asking you if you'd like to use iCloud. Follow the setup instructions, and you can connect to your iCloud account in just a couple of taps. If you don't get that prompt--or if you selected Later the first time you saw it--it's not immediately obvious how to start saving documents to iCloud; it doesn't appear as an option anywhere within the app.
In fact, the only way to enable iCloud if you previously dismissed that prompt is to head over to the Settings app. Scroll down and tap Pages from the list of apps. Once there, slide the Use iCloud switch from Off to On. Switch back to Pages, and you may briefly see arrows superimposed upon your document icons--they indicate documents yet to sync to iCloud. Progress bars will appear over individual document icons as the files are getting uploaded to the cloud. (Note that each app's Getting Started primer document won't sync to iCloud.)
It's an all or nothing approach: You either sync all of your documents with iCloud, or none of them. Once iCloud is enabled for a given iWork app on your device, you needn't think about it. Changes are saved to iCloud automatically as you work, quickly and seamlessly--as long as you're online.
If you're working offline--perhaps you're using the iPad to add to your novel up at 30,000 feet--you'll want to make sure to relaunch Pages once you're able to put your iOS device back online again. Close your current document by tapping the Documents button at the upper left, and you'll see thumbnail icons for all your files. Give it a few seconds, and the now-familiar arrow will appear to indicate that your file is syncing; when it (and potentially any progress bar) vanishes, you'll know you've updated the iCloud copy.
The only other major hitch to working with iCloud and iWork apps occurs if you try something you should really work to avoid: editing your document on multiple devices at once. iCloud can and will inform you if your copy of a document becomes out of date, and you'll see a notification if updates were made to a document as you're reading it. But if you make simultaneous edits on your iPad and iPhone, iCloud doesn't know which changes it should sync.
When that happens, your iWork app will pop up a Resolve Conflict alert. You can choose which version to keep as the master. If you choose to keep multiple versions, the app will create separate copies of the document, like Macworld article (Lex's iPhone) and Macworld article (Lex's iPad 2).
Generally, though, you'll only ever edit a document on one device at a time, so this shouldn't be an issue. If you know you made updates to a given document on your iPad, and don't see those changes immediately when you relaunch Pages on your iPhone, just give the app a moment to notice the updated version on iCloud. You can sometimes nudge things along quicker by tapping on that Documents button at the upper left, since that triggers iCloud to check for any new documents that it should display.
Thus, when things are working as they should, you'll never need to think about iCloud anymore; you can focus on your documents, while iCloud handles the syncing.