So I've been in coding classes since last September and my instructors have touched on but not thoroughly explained Git/GitHub -- all of my classmates seem to understand this and how to use it for their code, and when to use it for their code, but I'm lost. A few more direct questions that would be incredibly helpful if answered:

I can see how to create a repository - should one repo be for all of my projects or should each project have a separate repo? (What exactly is a repository? Is it like a folder on my desktop, or is it like the desktop and the things I put in it are like the folders?)

When I commit a project to be private, can I update it later to be public?

Should I be putting all of my projects on GitHub, or just some? How do I know which ones to post? (Is it a good idea to post my class assignments as that is the bulk of what I'm working on right now?)

Thanks for any tips/help!