This is very good explanation, but only explains what happens with the files, nothing about the graph what is a git repository. This talk helped me tremendously to finally understand what's going on in git: https://www.youtube.com/watch?v=1ffBJ4sVUb4

It is one of the best talks about git for beginners with an unfortunate title :D

Also, this interactive visual tool helped me to understand branching: https://learngitbranching.js.org/