Game theory is a math theory that studies competitive situations like economic decisions and elections. It looks at how people interact and make choices. Nash Equilibrium is when each player does best by responding to the others. There are different types of game models based on factors like the number of players and strategies. In normal form games, players choose strategies without knowing others'. Extensive form games show the order of actions. In coalitional games, the focus is on what groups can achieve, not individuals.