P2 takes a balloon and blows in it and holds it. P1 takes the balloon from P2 and let it go. Air is important. Well, yeah, for breathing. I think you're missing the point here.
Air is made up of gas molecules.
The molecules in a gas are constantly moving. When we put the molecules in a container, the air molecules bounce off the sides of the container. P2 takes a graphic with a balloon and arrows for the air molecules. In scientific language, we say that the air molecules exert a force on the balloon walls. A force is just a push or a pull - the air molecules push on the walls, forcing the balloon out.