Agree that diagrams would help clarify some points. I was a bit short on time for this so I thought that only using git outputs could be enough; I will try to spend some time to incorporate some illustrations!
If you do, I highly recommend avoiding the types of graphs that git draws for you and that some tools show. (The ones that show the branching history.) As a beginner, I found the graphs way more confusing than what was actually happening, as it didn't communicate anything I could understand. In fact, it made it look like something else was happening than what actually was.
Interesting. Do you think that confusion comes from the fact that commit history (to not say 'time') is represented vertically (and sometime going upward and sometime downward)?