The best way really is to follow the instructions GitHub gives you:
First, go the correct directory
cd <directory of your Xcode project>
It sound like you’ve already got a local Git project from Xcode. If that’s true, skip this code block.
git init .
git add .
git commit -s
<type in a commit message>
Last, push into your repository. The following is copied directly from my own github account, after I created a new “test” repo. Change the “dhalperi/test” part.
Push an existing repository from the command line
git remote add origin git@github.com:dhalperi/test.git git push -u origin master