I'm ready for silly AND good questions! đ Just so I can get it working....
I did turn on iCloud Drive in Preferences (it would not show up in Finder if I didn't....)
The only configuration I see is to turn on all the apps that can store to the cloud....and all are checked. (already were).
Didn't want to turn it off and on, because if you do it erases everything in the cloud and there's already a lot there from iCloud days (without the drive)
Oddly enough....after installing Yosemite on my old MacBookPro last night (2008 version)......I checked and iCloud drive WORKS on it. When I click on iCloud Drive in Finder.....the files stored there appear in the first column....and I can add files to it from Documents by dragging/dropping.
But....on my Mac mini desktop......it STILL doesn't work. When I click on iCloud drive in Finder....nothing happens. If I click Documents, all of it's files show in the first column. Then when I click on iCloud Drive.....nothing happens. It continues to show the previously checked folder (Documents) contents in the first column.
Why is it not working on the Mac mini is the question. The Mac Mini is 2 years old.....and has 16 gigs RAM.