puzzles on lichess are great. all the improvement stuff you have to pay so much for on chess.com is free on lichess. make sure at your stage you know how to checkmate without pawns… so, just a king and one two rooks, and a king and one queen. Once you do that, learn how to checkmate with one rook. They’re simple patterns that will be the exact same every time, and it’s embarassing (and common) to draw a game up a queen for free.
The opening you should learn for white is the Ponziani, GothamChess and Eric Rosen both have great videos. There’s a bit to learn and remember, but those openings really only have “theory” a few moves deep, so, it’s really not much, and there’s great traps which make them easy to remember but also teach you tactics.
At 500 - 1500 the most important thing is tactics, strategy, and knowing how to win when you’re winning (aka getting checkmate, not stalemate/draw). Not openings. Puzzles are great in general to show you what you’re good at and not good at… and there are so many different “types” of tactics that really it’s just easier to hit them with rote repetition instead of formally “studying” them.
Chessable has some really good free courses.
This one is for openings. It’s all about WHY openings are the way they are… you’re too early and low ELO to memorize reams of theory, but this will help you make decisions when you haven’t memorized what the right move is. Hint: you should never know, at your stage, what the right move is. Don’t even try and study a opening for black, just use the fundamentals and figure it out.
These “(Piece) on the attack” courses are excellent for general gameplay and finding great explanations for lots of really “simple” scenarios that are NOT so simple.
This is an introduction to tactics course
And this is a great endgames course.
2000 is a very very advanced rating so just be mindful of your expectations vs reality. If you hit 1200 by spring or summer that’s definitely do-able but already a huge growth curve. To go from 1200 to even 1800 is 10x harder, and to go from 1800 to 2000 is another 5-10x harder. You can do it. You have subliminals. But once you hit 1500 don’t be surprised or ashamed if you don’t care anymore, lol.