Dispersal is the act of spreading something around. This could be positive (like a dispersal of money) or negative (like a dispersal of a crowd because of a bomb).
If you know that dispersing is when something spreads out or separates, then you have a headstart to understanding dispersal. Dispersal causes something to be diffused or disseminated, like the dispersal of seeds in a garden. A strong wind could cause the dispersal of someone’s homework. A tear gas bomb causes the dispersal of tear gas, which in turn will cause the dispersal of a crowd. Anytime something is spreading out or becoming widespread, there's a dispersal at play.