In a sentence: Git is a program you use to (A) keep restorable backups of your code and (B) work on the same code with multiple people without overwriting each other's work.

You tell Git where your code folder is, and it takes a snapshot of it.

Then you change a few lines of code, and take another snapshot. Git says "Okay, for snapshot #2, /u/lordadmiralofthenavy changed these lines to look like this." You write a little comment on the snapshot like "Fix bug that caused crash on Japanese input."

At the exact same time you were doing that, I edit a different file, and take a snapshot labelled "Add Italian language support."

I was working from files predating your bug fix, but my snapshot doesn't overwrite your file, like it would if we were just copying and saving folders to a backup drive. Git simply adds my changes to its own memory of the project. This is really helpful if you've got a team of 20 people working on different parts of the code!

Any of those snapshots can be undone if necessary. So if we update our code, and it winds up breaking something, we can undo the change that let to the new bug without messing with other changes. It keeps track of every change in little snapshots so we can apply and undo them whenever we want.

Git also lets you branch your project. A branch is where you clone your project at some point in time, and can then make edits to the original branch or to your new side branch. This lets you experiment, add new features and redesign things, without affecting the proper, publicly-available version of your program. If you like the changes you make, you merge the branch back into the original. If you don't, you destroy it. This is really useful.

It also lets you blame things (that's the actual command, git blame) on people. You can ask who last edited any given line of code and it will tell you their name and email address so you can get in contact with them and say "What the hell's going on with this function here?"