Suppose that you want to work in a repository that exists in a server or in the cloud. You cannot commit directly there. You need a local clone of that repository.
GitHub recommends accessing to repositories by HTTPS URL, SSH URL is also available if you prefer. See this GitHub help page if you have troubles with authentication.
We will create a local repository in the folder c:\projects\makingsense.github.io
cloning https://github.com/MakingSense/makingsense.github.io
cd c:\projects
git clone https://github.com/MakingSense/makingsense.github.io.git
cd migration-to-git
It downloads a full copy of the remote repository into the selected folder (.git folder), prepare the working tree and also configure a remote repo named origin. In this local clone you can fetch other people commits and push yours.
If you want to work with more that one remote repository see configure remotes.