None of this helps you understand how merging works, of course. Pro Git is great at telling you mechanically how to merge, but doesn't explain at all what can go wrong, and I don't think it actually describes the merge algorithm anywhere (certainly not in the main body of the book, or the section on Internals).
I still have to look up the order of arguments for commands like git rebase, but overall, it makes complete sense.
I can really recommend "Pro Git" by Chacon and Straub. I got a printed version, but it is also available under the CC-NC-SA here: https://git-scm.com/book/en/v2