Jerry's method for making new versions by clicking the Filename at the top is nice; now I understand a little better why Apple tried to mess with Save As...
Choosing the Move to iCloud... option from the Filename will move the document to the right place in the Library, saving a trip to the Finder. After a document is placed in the right folder in the Library, it gets whisked up into the cloud and synced it to other devices connected to that iCloud account. Then a change to the document on any of the connected devices is synced to the other devices, keeping them all updated to the "latest version."
In my experience, with Numbers that syncing of the latest version across machines works really well...
... except for when it doesn't, such as during the five or so days after the iOS 7 update when iCloud mysteriously locked out some users, including me.
In the end all my documents reappeared out of the ether as mysteriously as they disappeared. But now I'm more careful to make reasonably frequent duplicates of really important stuff. The duplicates become quickly outdated, but they are nice to have when there are glitches up in the cloud.