Git is a version-control tool used to track files and sync them across computers.
Git is handy because it keeps backups of project files over time, both on the cloud and on your system.
If you make breaking changes but don't realize until after you did some other stuff, you can simply revert only the breaking changes, while leaving other things unaffected.
If your hard-drive crashes and you lose all your files, they're still backed up on the server. Even if the server *also* crashes, anyone else working on the project will still have the entire project history stored on their machine, which can then be pushed to a different Git server to continue collaboration.