Git makes it as easy to create a private repo as getting a checkout of the source code. In fact, that is all you have to do.
git clone http://git.sxemacs.org/sxemacs
You may want to follow some of the steps in See Automating with Aliases, to ease your life when sending patches if you plan to contribute frequently from this repo. Please note that in this case you should not reference any REPO-URL.
However if you do plan to contribute frequently, we strongly suggest you configure a publicly accessible repos.
More details at See Setting up a publicly accessible repo.