macOS folders

newbie question, so bear with me...

iCloud seems set up by default to upload files from a range of folders as well as from the desktop.

One first question: is it possible to NOT let iCloud upload files from the desktop? it is such a convenient place (for me at least). when I import, say 40Gb of videos on my machine, I'd like to be able to keep them on my desktop if I feel like it, without them being uploaded to iCloud. Yes, I've worked out that if I drag my video files to the 'Movies' folder they won't be picked up by iCloud (hurrah!).

Storing audio files

I'd like to create a folder for audio files. So, what would be the best place on MacBook to create the folder (unless there's one I've missed?)? and again, a folder that would NOT be picked up by darned iCloud.

Last but not least, anyone can advise on the best manual out there to make sense of the macOS filing system?

Many thanks!