ICloud Storage...

You can't use iCloud for general file storage in the manner of the defunct MobileMe iDisk.

iCloud:

Provides one main @me.com email address and up to three 'aliases' (additional addresses).

Allows you to sync your calendars between your Mac(s) and iOS devices.

Ditto with contacts

Ditto with Safari bookmarks

Provides a conduit which copies photos taken on any one device onto all the others

Provides a fairly basic photo gallery (populated only from iPhoto for iOS)

Provides 'Find My iPhone/iPad' to locate a missing device that is able to connect to a network

Backs up the contents of your iPhone

Syncs iWork and TextEdit documents (only) between your Mac and your iPhone

Tracks the location of your friends (only with their permission)

More details with illustrations and videos here:

http://www.apple.com/icloud/what-is.html

If you want to store copies of arbitrary document types in iCloud, so you can sync them with other macs, look at this user tip by Winston Churchill:

Using iCloud to sync multiple document types.

I am syncing Filemaker databases, folders with photos, and LaTeX documents this way between my macs.