Our assumptions now allow us to gain a deeper understanding of Boyle's Law. To recall, Boyle's Law states that for an ideal gas, when the pressure is increased, the volume will also decrease. Conversely, if the volume is increased, then the pressure will decrease.
A container that has gas in it has its walls constantly bombarded by the molecules inside. This unceasing bombardment exerts pressure on the walls - remember that pressure is defined as the force per unit area. If you reduce the volume of gas in the container, the molecules will move closer together and strike the walls at a more frequent rate. For example, if you reduce the volume by one half, the pressure will double. Twice as many molecules will hit a given area of the walls per second. This of course is Boyle's Law!
