Use Atom to open on-line repository

First of all, learning to use both Atom and GitHub. I went on GitHub’s website and created a repository, went through the standard Hello World tutorial but I was wondering how I can open up that repository’s code within Atom on my PC? If someone has an easy step by step to throw out there I’d appreciate it. I’m really hoping to learn how to use this and Atom as quickly as possible - recommendations of helpful textbooks, videos, etc…, would be much appreciated as well.