Since Git is peer-to-peer, you can actually host your central repository anywhere that all your users can access it. However, if you don't already have a Git solution, we strongly recommend using the free GitHub, which is now owned and managed by Microsoft. It is reliable and easy to use, and provides the excellent GitHub Desktop program for creating your local working copies and external management.
GitHub is managed by Microsoft, which now also uses Git for its own code management. However, it was originally an open source development and even before being taken over by Microsoft it was firmly established as the leading site for hosting projects managed under Git, both privately and publicly.
GitHub is the result of the same development philosophy as Git itself, and it is just as reliable as the entire Git system. It is completely free for most needs, and highly accessible internationally, with excellent transfer speeds. It can be used both publicly and privately, and it is very easy to give users access to the projects hosted there when needed.
The free GitHub Desktop program is an excellent, multi-purpose Git GUI that can be used for managing Git repositories hosted anywhere, not just on GitHub. If you don't already have another solution we recommend it.
In this documentation, all Git GUI operations are described for GitHub Desktop. However, the basic principles are the same for all Git GUIs, so if you are using a different system the instructions should be easily transferable.