If you already have a github setup (meaning you have an account and created an empty reposity with that account), this is how you add github to htis folder:
cd ~/project_folder # Go to the folder that you created where you want your githubt to pull from
git init # This is initalizes the reposity
git add . # This adds any files in that folder
git commit -m "message about initalzing folder" #This tells users of your github account (and older versions of yourself who wonder "what the f*&# was I doing when I did this?) about the files that you're adding and any changes that you made. More specific > less specific.
Go to your github page, then copy the link, then:
git remote add origin [copied link]
Volia! You have your github account setup!