At its core, the difference between a Player and a Game Master (GM) is a matter of scope. Think of it like a movie: the players are the lead actors, while the GM is the director, screenwriter, and the entire supporting cast.
A player is responsible for a single character. Their goal is to inhabit that persona, make decisions based on their character's motivations, and react to the world around them.
The GM (also called a Dungeon Master or Narrator) manages everything else. They don't “win” or “lose”; instead, they facilitate the story by describing the environment and playing every person the players encounter.
The Golden Rule: While their roles differ, they aren't opponents. It’s a collaborative effort where the GM provides the spark and the players provide the fuel.