Mac OS X comes with a version of Git baked in. This is convenient, but it is generally always out of date. You can check to see if your version of Git is current by typing "git --version"
But what can be very confusing is that if you installed Git, you might actually be running the built in version.
Step 1: How To Know Which Git You Are Running
If you type "Which Git"
The command line interface will report which install of Git you are running.
If you installed Git (which I recommend) you should see something like "/usr/local/bin/git"
If you are running the Apple version you will see "/usr/bin"