I've put up another video on groff/troff where I briefly talk about more basic formatting with the ms macros, but also how to create and implement macros of your own.
Since it's hard to get good documentation on groff/troff, I'll also provide some links: check out https://www.troff.org/ for general information. A user also posted a very useful .pdf which is a general guide to Unix test processing, but contains decent chapters not just on groff/troff, but also on its preprocessor programs like
eqn (equivalent of math mode in LaTeX) and
pic (equivalent of tikx).