iCloud is the service that allows you to sync your music, your documents, store all of your backups, etc. You can even restore straight from iCloud, eliminating the need for a Mac or PC.
iTunes Match is the service that piggybacks on iCloud to allow you to upload and stream your music from anywhere.
We’ll be back with full walkthrough of each service once they go public. Remember October 12th for iCloud and iOS 5, and late October for iTunes Match.