Hello, my question is how to face Game Theory concepts.

Game Theory:
- is a theory that explains how people normally behave in competitive
situations (ie, explain a phenomenon), or
- is a theory that, once a person knows it, he/she start behaving
differently to better compete, and has advantage over someone who does
not know the theory?

I know the game theory models (prisoner's dilemma, dominant
strategies, Nash equilibrium, strategic and extensive trees, etc). I
wonder if there is a specific answer, or literature, for my question.

Thanks!