There's a lot of documentation on the web for Git, but the Git/Github integration can get a little hairy if you get out of sync.

The pull request workflow depends on what you're working on (Personal project? Company project? Massive open source project?), but Red Hat has a pretty good overview of a fairly standard system that most people should be familiar with:

https://openshift.redhat.com/community/wiki/github-workflow-...

If you have any more questions, feel free to shoot me an email, I'd love to help you out.