When someone sends you a pull request from a fork or branch of your repository, you can merge it locally to resolve a merge conflict or to test and verify the changes before merging on GitHub.
This page gives brief, visual reference for the most common commands in git. Once you know a bit about how git works, this site may solidify your understanding.
bitbucket is a hosting site for the distributed version control systems (DVCS) Git and Mercurial. The service offering includes an issue tracker and wiki, as well as integration with a number of popular services such as Basecamp, Flowdock and Twitter.
This is the website for the Pro Git book, written by Scott Chacon and published by Apress. Here you can find the full content of the book, a blog with tips and updates about Git and the book and open source projects related to Git or referenced in the book.