Honestly? There's three, maybe four, routes to getting started with understanding the system of d&d. If you go with another brand of game, those might shift a little, but mostly don't.

Path one is to find a beginner oriented DM/game. The rule set for any given edition of d&d is best learned with help, and nobody will do that better than an experienced DM running intro tables.

However, route two is to do the opposite. You become the DM and round up a table of anyone you can con into playing. You read the core rules, and dive in head first. As long as everyone playing is aware it'll come with a shit ton of errors and fuck ups, it's a very fun way to get going.

Two B is to do the same, but as a player rather than the DM.

Route 3 is to go all scholar about it. Obtain the books of the edition you want to play, and study it like you'll be getting paid to play. This is more viable nowadays since the more recent editions are written up better. It helps that YouTube and forums exist as well, because you aren't limited to just what's written by the company. You can get explanations.

Route four is some hybrid. Obtain the core books, read them, then go looking for a group to play with, be sure they know you're a noob, and back that up with plenty of reading and video watching as you go.

The central idea of d&d is a big game of pretend, but with a mediator to keep things sane. Everything else is window dressing ;)