How to sync your Mac desktop via iCloud

MackBook Air desktop is synced via iCloud
MacBook Air desktop is synced via iCloud

I'm pretty sure you once had been in such a hurry in the end of a working day when someone gave you a file from USB stick or e-mailed it. You just did nothing but put it on your desktop. Okay, but how to take it back from the office computer?

You can sync your desktop contents through iCloud Documents!
Bonus: since iCloud free space is just 5Gb, you are not going to litter your desktop with huge files :)
ok, how to set it up?