Please get git for tfs from the following location.
To clone a repository in tfs just execute the following command,
git-tf clone http://your.server.name:8080/tfs $/sourceToClone
Then fire up your favorite git explorer - probably SourceTree. Click on "Clone/New" button and enter the destination path in the field called "Source Path / Url"
Click "Clone" when done.
You can see that your tfs repository is cloned.
More documentation can be found here.