[rcthompson]

Well, first you need to get started with Git, if you haven't already done that. Github itself provides links to Git tutorials.

Anyway, many projects on Github use Github's issue system for tracking bugs and feature requests. So if you find a project that you are interested it, see if it has any outstanding bugs in the Issues section that you think you could take on. Then fork the repo and try to fix the bug. Test your fix to make sure it works, then submit a pull request saying that your fork fixes the bug.