Essentials.
learn how to write and read. (optional.)
after that. You need something to write. (required, unless you can just tell someone to do it for you.) prehistoric humans usually drew on stones but since you are reading this. And are most probably somewhat literate (probably far more than i am.) you can actually write it! you just need something to write. A piece of wood lit on fire can produce charcoal wich can function as a makeshift pen. It can also work on stones. you can also find a pen or carve letters out of something. Truly your own imagination is the limit. You can already gather some good bonus points if you have something unique that you write on and how you do it. But i wont go into detail, since this is a guide to writing a book. Not making art.
you need a chapter structure. even if you can skip it, wich i cant recommend since i never tried it myself.
Your chapter structure can be quite simple. Either making chapters just points or areas in a timeline going from start to finish.
or you can take an absurd approach of writing in the most convoluted unimaginably hard to read way. Where you start in the middle and jump across different points in the timeline. Wich can be quite fun if you do execute it effectively. But that’s as easy as trying to move around a city during rush hour. (might as well give up or just get in an accident to get a valid excuse.)
with having a chapter structure figured out. You probably need to figure out how to write your story. Well you can take a few approach to do exactly just that.
You can either.
try to figure out how your story goes, figure out its characters. set plot points, have a well put together plan. And write according to it, adding small details wich will extend the books value and page count.
Or!
You can get high and sit down to writing. (even though this method has lost popularity nowadays since the stigma around drug abuse. It was used over ages by writers all over the world to create shocking and valuable stories, with that i’d like to say that my stash ran out.)
after you write the story. You have to publish it. (this segment was never finished.)
after having your book out there. You need to form an opinion about it (aka you have to read it again). It is entirely up to you. But what i’d recommend is.
“Love it and think of it as the best piece of art ever written which will be taught in schools for ages. as an example of an excellent classic.”
“Its so fucking dogshit. I might have burned the tree that I wasted on that book to warm myself in the midst of summer. I don’t know why I would ever publish it.”
Bonus points if you alternate between those two constantly when referring to the same book.
And that concludes what this chapter needed. AKA Essentials of what you need to write a book.