Gases exert pressure on surfaces with which they come in contact.The pressure that a gas exerts on a surface is the result of gas particles colliding with the surface. Since the gas particles move randomly in all directions, they exert pressure equally in all directions.If the volume of the gas is kept constant , its pressure increases with the increase in temperature.
For example, when the air is suck out of a bottle, the air present out side it exerts pressure in all possible directions of bottle . Due to this reason the bottle gets crushed.