$ git clone <repo url>
That's really it. There isn't much more to this. By running the command above, this will tell Git to go to the URL and pull all the codes to your local computer.
To get the URL, go to the Github repo and in the lower right hand side there will be an aside with the title of HTTPS clone URL
Simply copy the URL from the text field, an example from the Node project is:
https://github.com/joyent/node.git
And there you have it, you own all the codes!