I have come to think that while setting up the server is easy as can be, the how-to makes it look quite difficult.
Hence i added a short summary:
0) Ultra short Summary
Install gitolite on the server and add a user called git
Install git on the client and copy your ssh-key to the server
Make a bare git repo on the server
clone it from the client and set the server to be the remote repo
start pushing and pulling from the existing master branch