what happens to each computer's version of folders when activating icloud

new to all of this, so question is unclear. I have two Macs now. when I activate desktop and documents in iCloud, what happens to the different sets of files on each computer's desktop and documents folders?

Thank you for replying. I'm trying to get to the point where both computers' desktop and documents folders are synched. Once I flip the switch on each computer, it sounds like I'll have two desktop folders instead of one sitting in iCloud. Is this correct, and if so does the article mention what to do next so I eventually end up with one desktop folder synched between the two computers? The article talks about accessing Mac desktop files from iPhone and iPad which have no desktops, but in this case there are two desktops so it now seems unclear that synching desktops actually happens.

That's not what I was hoping to hear. Is there any way to sync the desktop and/or documents between two Macs? That's what I was hoping to achieve.

Thank you both for helping me understand this concept.