Git-Flow is a collection of Git extensions to provide high-level repository operations for Vincent Driessen’s branching model.
You can get a brief introduction to Git in my article Getting started with Git.

Git-Flow can be found on GitHub: https://github.com/nvie/gitflow

Mark Derricutt made a short introduction to Git Flow:

A short introduction to Git Flow from Mark Derricutt on Vimeo.

Dave Bock made a screencast showing how to use Git-Flow:

Oh The Path with Gitflow from CodeSherpas on Vimeo.

Jeff Kreeftmeijer posted ‘Why aren’t you using Git-Flow?’