These were a big part of how I learned git. Do check out his git internals book; the material in it is basically what's in the 'casts, structured along the lines of his RailsConf talk: http://gitcasts.com/posts/railsconf-git-talk

The approach he uses is very similar (a little bit more detailed) to this tutorial ("Understanding Git"): http://news.ycombinator.com/item?id=531517