What functions do pheromones perform?

Pheromones are very important chemical messages that animals use to communicate to each other. Generally, pheromones tell animals of the same species a) the state of reproductive readiness (Male elk for example can tell if a female is ready to mate by smelling her urine to see if there are certain pheromones present indicating that she is ready) or b) the emotional state of the animal (sometimes fish release fear pheromones into the water to warn other fish of a predator)

Pheromones are typically inhaled by animals, and the brain determines what the pheromone means. Even humans can interpret what a pheromone means, even though we are not really aware that we are smelling a pheromone.