Any help would be great! Thanks!
pressure is force per unit area. when you pump air into a tire, the air particles move about and hit the wall of the tire. as you pump more air into the tire, more air particles hit the wall of the tire. thus pressure increases in the tire because when the air particles hit the wall of the tire, they exert a force on the wall.
the air has nowhere to go and as more air is added, pressure goes up. if it could escape through a hole, it might remain the same as you pumped more air in.