But let's say we were to play Stonetop (a PbtA game): the GM would provide the players with a cheat sheet reference of game moves plus playbooks, which have everything that you need for your character. There would be no need for you to buy this material. No need for you to look up character creation rules in a player's book. It's all there on your playbook.
Resolution System = Roll 2d6 + Mod. Describe what you are trying to do in the game world. The GM tells you if your actions trigger a move, and then you roll for that move. If you roll 1-6, you fail and the GM makes a hard consequence. If you roll 7-9, you achieve a complicated success, and the GM makes a softer consequence. If you roll 10+, you achieve a full success.
Got that?