Kickball is a sport similar to baseball, in which you use your hands and feet instead of a bat. But of course, you need to know how to play baseball in this case.
So basically, there are two teams. One person from one team throws a ball special for kickball (similar to a football but softer) to a person from the other team. That person has to kick the ball as far as he/she can. Then the other team will try to catch the ball while the person runs to bases, and then other person will kick, and the team has to run trough all the bases.
Here you can listen to the full explanation: