I don’t about it’s page count, but the goto-place for your need seems to be the “Introdution to Programming in Emascs Lisp” which is reachable from emacs with C-h i m Emacs Lisp Intro

It is structured nicely, so you should be able to find the relevant parts easily from the table of contents, you don’t have to read it all. None the less I would recommend to read as much as possible, because it’s very informative and (in my experience) well worth it.