Files deleted from desktop after starting"iCloud Syn"

Craziness....almost Microsoft like. I clicked on iClouid sync and all files went to iCloud but dissapeared from my desktop. I teach and often dont have WiFi so need the files ON MY desktop. Where was the warning that turning on "sync" would delete the files from my computer? Why would syncing something delete files? Syncing indicates to me that we make things alike, similar, a mirror image if you will. Deleting things makes things different, not in "sync" anymore.

When I try to move files from iCloud as other discussions suggest, and unclicking my files in iCloud sync, I get a waning that there is not enough disk space on my computer. How can that be if I am merely restoring the same files that were there.

Help, I have a lecture this week end.