What is Github? Good question. First, let's discuss Git.
Git is an open source version control system. Let's unpack that.
Open Source : Freely available to the public. Think of it as the antithesis of copyright. Anyone can edit, share, and use the code!
Version Control : Think about your favorite app. How do you think new features are being developed without breaking the app on your phone? How do you think multiple coders are working on the same project? The answer is a version control system (and its almost certainly Git).
Okay what about GitHub? Think of it as platform that uses Git. It adds features like repositories, forking, social networking, and more. Repositories is "tech-speak" for project folder. And forking lets users copy any public repository so that you can use and work on other people's code. Neat, right?