Whether to fork your repo or just clone and branch depends on your workflow. If you want to manage your project like a centralized system, then simply have him clone your repo locally on his machine using:
git clone https://github.com/username/your-project.git
Then he can make a branch and request that you pull from his clone. If you want to try the distributed method of source control management, then have him fork your repo. Then he can clone, make changes, push to his fork, and then send you a pull request right on github. I recommend forking because pulling from another machine seems a little more complicated and because github has some very nice features for displaying the changes that have been made. No matter which way you do it, I would recommend branching, making your changes and then merging back to master (you can see the reasoning in the answer to this question).
Oh.. also question for my own sanity.. I should be working off a branch off my own master.. and how does that effect the local files when I switch through branches
When you switch branches, git removes all your previous branch's commits and changes from files and then adds all commits and changes to files from your new branch. Also I recommend checking out the git documentation. It should be able to answer basic questions about how git works and how you can get started using it.