Version control is a rare tool that I would say is absolutely required, even if you are only using it as a solo developer. Some people say that it's a tool that you live and die by, I agree with that assertion.
Version Control is a dummy useful class of software that has helped me out countless times. Atlassian has a pretty good overview of what it is and how it generally works.
For the uninitiated, it's basically where you use a software to semi-manually keep track of changes you make to code, text, or anything really. It will see that a file has changed, you type in a comment to help you remember what you changed, then you save it to a "repository" where you can recall every single change you've recorded. Usually, this repository will be hosted on a server, like or or whatever, but it's not a hard requirement.