Practical Emacs Lisp
This chapter teach you how to write emacs commands (that can be called by M-x) and how to write emacs lisp script that can be run in a terminal.
This means, you are learning many emacs lisp functions that deal with issues related specifically to emacs, such as buffer, mark/kill-ring (clipboard), query user by prompt in minibuffer, find replace string in buffer, moving cursor, cursor position, etc.
you might start by watching a video