I'd like to start using and contributing to github, how and where do I start?

Find some community project in github that relates to a language that you know well. Smaller projects might be better as it will be easier to understand. If you think you can add a feature or fix a bug then do it and then do a pull request.

Could start your own as well. @pxgamer is really good with GH

You start by creating a github account.

There's a list of contributor friendly repos on the showcases page I think