Note that Apple lets only apps sold through the Mac App Store use iCloud to store documents. If your favorite productivity app is only sold directly by the developer, you're out of luck.

If you're using an application that can save documents in the cloud, doing so is fairly simple. Say you're using TextEdit. After you've created a new document, press Command-S, and make sure the Where menu shows iCloud. Name the file and click and the document will be sent to the cloud.

Once you've saved a file to the cloud, you can access it from multiple devices. Say you have a desktop Mac and a laptop; you can save any files you need on the road in iCloud and access them from either computer as long as you use the same app.