Open up a terminal or something that can run git commands and cd into the project directory. Connect your email/github username if you haven't, copy the link to your repository, and run these commands:
git init.
git add .
git commit -m "message here"
git remote add origin
git push origin master
This creates a repository on your machine and links it to your github repository. Then pushes all your files onto it.You can verify it worked by refreshing github, or with the command:
git remote -v