I recently took a class where we decided to use Git for a group project and that is something they don't teach in class (I don't know why). I just took the Git tutorial for fun and to refresh and learn anything I did not know since I only did basic operations and someone else maintained the commits, merges, and master branch. The course is very thorough and I enjoyed it.
My only suggestions would be to show the user on the merge and branches portion a network graph like they have on GitHub. I know this is briefly shown but maybe more frequently would be useful and after steps that would alter it. This would be helpful to show how their branches can be ahead of master or get merged into master. It is just a visual thing that may bring some more clarity to others.
Thanks all for reading and I hope you enjoy the courses as much as I do!