Check if you have git installed with git --version. Hopefully you have a version greater than 2.2. All mac computers come with git installed. The versions will change based on the version of you operating system.
If you don't have git there are a few options to install. I think the easiest is to use homebrew. I'm not going to explain how to use homebrew here, follow their documentation. Once you have homebrew working install git with brew install git. Then git --version to see if it is working. You may need to restart your terminal to get it working correctly.