git - creating git repo for my site and edit permission setting

Question

1. how do i create a git repo using my site files in my shared hosting acc (like - say files located in my hosting for sub domain site - http://mysite.maindomain.com/) so that i work with that git repo by cloning it in my local hard disk as this is the way working with git is done,so changes(commits and then push) in those files will reflect in my joomla site http://mysite.maindomain.com/ i once saw this kind of repo url becomes like this one for cloning - devaa1@20.18.26.241:/var/git/devaa1/public_html

2. how do i set permissions so that whom i gave permissions only can clone my git url locally and can push to my git repo for changes. i added some test collaborators from my git repo options and it works fine online that only those collaborators can edit git repo files but i tested that when i clone the repo in my local hard disk i can push with no problems!! how to avoid it.