Happy to explain a bit more about GitHub!
At its core GitHub is a source code host for anything from web applications to homemade spacecraft. GitHub works best when you use it to share your work with other people but we make no requirement that you do so.
If you want to restrict access to your source code we do offer private repositories with our paid plans. If you're part of a company or organization we have Organization accounts that make keeping track of permissions and collaborators easier.
For more information check out https://github.com/features.
Hope this helps! And welcome to the GitHub Community Forum!