Git

Git is a tool for keeping track of your code. In all types of development (web sites, web application programming, software) Git is used to check in changes in your code as it develops. It was created by the inventor of Linux (Linus Torvalds) to keep track of collaborative projects but I use it for solo work too. If you accidentally delete an important file or you want to roll back recent changes, it's all possible.

I strongly recommend that you create an account on github, if you haven't already. It's free of charge. Microsoft bought github a few years ago which put a lot of noses out of joint, but I don't really care if someone else sees my code, so I'll keep using it. I suggest you set your account's security settings then you can have them host your development site free of charge.