Visualizing Git (Repo) and the website which has some interesting scenarios built in to practice with. On the website I just suggest zooming out a bit as things are a bit crazy. Unless you’re one of those rich folks with a massive monitor!! 
That repo is based off of Explain Git with D3 which is also worth checking out.
Github’s Try Git … which I still need to try! 
And a piece of software that is visual and free: Gitup