Take a tin can with a lid and fill it half with water. Heat the can on a candle flame till the water boils. Let the water boil for a few minutes and immediately put the lid tightly on the can. Pour fresh water over the can. You'll see the shape of the tin box changes. This is due to:
Pressure inside the can is less than that outside
As water is poured over the can, some steam in the can condenses into water, reducing the amount of air inside. The pressure of air inside the can is less compared to the pressure exerted by the air from outside the can. As a result, the can gets compressed.