This doesn't start with the plumbing commands, but it's along those lines and seemed helpful to some new-to-git folks at work when we started switching to it last year: https://eagain.net/articles/git-for-computer-scientists/

If you're already comfortable with git, the Git Internals section of the book may be better: https://git-scm.com/book/en/v2/Git-Internals-Git-Objects