Emacs has built in documentation. Learning emacs lisp is a good start: https://www.gnu.org/software/emacs/manual/html_node/eintr/index.html https://www.gnu.org

Emacs has built in documentation. Learning emacs lisp is a good start: https://www.gnu.org/software/emacs/manual/html_node/eintr/index.html https://www.gnu.org/software/emacs/manual/html_node/eintr/in... This manual is also the part of the emacs distribution.