Reading this[1] and getting the data structures/mental model correctly internalised in my head.
Although I do use git from the cli (or magit) primarily, this knowledge has helped me pick-up front end tools intuitively and have helped others when I've never used their preferred tool. All of this doesn't seem possible unless you've put in the effort learning what's going on behind the scenes. That is to say, git itself it neither user friendly nor intuitive it must be learned.
Knowing mercurial (hg) beforehand did slow my learning progress a bit with all the false-friends. You may find it easier to learn if you don't have to re-learn some naming.