Ah you're entering the magical and enormous world of git!

Git is a tool you can use on a filesystem (Mac Finder, Windows Explorer, etc) that basically turns folders into powerfully augmented things git calls "repositories".

You have a folder of files / code / whatever. Git let's you take "snapshots" of the current state of that folder and everything in it. Like saves in a video game. "take my whole set of files and call this Save 1”. Now you can make a bunch of changes and either create Save 2 or rollback to Save 1. You can even go back to an even older save and start a whole new "parallel branch of history".

This is how software developers do things like maintaining different versions, making broad changes and then only keeping the bits they need for a small update, trying stuff safely without having to "undo" a billion times, etc. without losing our minds.

That's git. "GitHub" is a website that allows people to take their local augmented folders (remember they're call repositories or repos) and pop them up on the web. Now other people can copy (clone) those repos for their own use. Or for making changes and then submitting their updates back to the original owner (and since all that excellent history-tracking stuff I mentioned is there, making sense of other people's changes and how they fit in is much easier). GitHub adds a bunch of sharing and collaboration tools on top of that basic git repository / supercharged folder concept.

You'll soon realize that nearly the entire world of consumer software is built with GitHub helping organize collaborators, and each individual developer using the git tool on their own computer to make changes in an orderly way.

Whoa, right...?

Let me know if you have questions!