I didn't understand how git really worked, and I was curious. Since I also have to work with git every day, it seemed sensible to learn a bit more about how it works. I'm not a particularly advanced git user; I mostly stick to the basic commands 'checkout', 'merge', 'pull' and 'push', and occasionally 'rebase'.
I bought How Git Works from Julia Evans. This is a great introduction to how git works; it's very accessible to me and I like Julia's writing style.
I prefer to explore and experience, rather than simply read about a subject, so I was happy to find Write Yourself A Git. I've been working through it in zig.