To make a crowd at a party disperse, you could take away the food, turn off the music and ask for volunteers to clean up. Disperse is to spread out people or things, making them move in different directions.
Imagine yourself standing on a basketball court holding a cup packed tight with marbles. If you turn it over, the marbles will disperse across the floor, moving away from you in all directions. Another word for this is scatter. Don't confuse this word with disburse, which means to distribute money. Remember that false friends disperse when you cease to disburse.