Depends on what you want/expect and what your experience is with the hobby.
If you already play tabletop games, and have an idea what kind of rules work and what don’t, and you’re just making a game for your own group, it can be pretty easy.
If you wanna make a commercially viable product, it’s going to be harder of course since a lot of extra factors come into play like who is making the art, the layout, the editing (NEVER EDIT YOUR OWN BOOKS! Always get a second pair of eyes to do the editing.), how you’re gonna handling marketing, distribution, etcetera. And even systems-wise some things will become important that aren’t important with a personal game, like system licenses (OGL, CC, All Rights Reserved, …) and game balance becomes a lot more important as well in a product you’re exploiting commercially.
If you’ve never (or only rarely) played games before and want to make something to play with friends, it’s going to be rough, but I’m sure you can make that work. It’s what people in the past did and while the very first designs of tabletop games were rough, there’s still people 50 years later who swear by them, so they can’t be all bad.
But if you wanna make a commercially viable product while having no clue of what works and what doesn’t, honestly, I don’t like to step on dreams, but I’d recommend to play games online for a few years and then try again. If you don’t got friends who like to play then visit LFG forums or whatever fits.
It depends on several things.
First, how do you treat your game nights? Do you treat them as a casual social gathering where it’s ok to show up fashionably late; or to not show up without warning; or to drop out last minute because of whatever non-emergency reason? If so, don’t be surprised players also treat it as something casual and social, and reading rules isn’t casual or social. Maybe D&D just is too complex and not the right game for your table if you just want to run a casual social event.
Personally I treat my D&D style campaign game nights similar to how I’d treat coaching a sports club. If you want to be a striker on a soccer team, and you don’t understand the off-side rules and don’t want to learn them, no coach in their right mind wil put you on the field either. Sure I give my players time to learn, and don’t expect them to know everything from day 1, but the absolute minimum I expect is a willingness to improve.
Practically, what I do for each player in my campaign is to compile a document which I expect them to focus on. They roll up a fighter, I will include the fighter class entry plus common special maneuver. They roll up a wizard, I will include the wizard class entry plus their spell book. They roll up a merchant (which I consider the most complicated class in my game and will discourage inexperienced players from taking it), I will give them the class entry plus a 101 intro to the economics of my campaign world. They have 3 months (approximate 10-15 weekly sessions) to understand the material I’ve given them, before I start reconsidering their presence in my campaign. Obviously there’s some flexibility, it’s not a life or death matter; but again I do expect at least some sign of willingness.
Next, please do understand I did specify campaign game nights above. Obviously things are different with one-shots like convention games or open table games at the local game store. I don’t expect the players to know any rules there and will happily guide them by the hand from start to finish.