how to create a pull request on GitHub
Explained step by step here: http://stackoverflow.com/questions/14680711/how-to-do-a-github-pull-request/14680805#14680805.
In short: fork the repo you want to contribute to; clone it to your local machine; do the changes, commit, then push it back to your repo. Then create the pull request on the web interface of github: visit your repo and click on the “pull request” button. Fill out the necessary information and create the pull request. The project’s owner will be notified about your contribution.