Summary
Servers
A Git server represents a machine that has Git installed. A server holds multiple Git repositories that you and your team can push and pull changes from.
A Git server can be a server that you have setup yourself, or it may be that you use Git as a service. Some examples of Git as a service are GitHub, BitBucket, GitLab, Visual Studio Team Services, etc.
All types of git repositories are treated the same by Git for Confluence. We are using plain git via http(s) or ssh to access your server. We are not using specific API from Github or Bitbucket for example.
Chances are you are already using git and want to get going with Git for Confluence. First things is to setup your server(s).
Repositories
When you have setup your server(s), next thing is to setup your repositories. This is also the place where you configure who has access to the content of your Git repository.