Watch a mighty invisible hand crush a milk jug.
Usually hot things expand and cold things contract. Water is one of the few things that expand when frozen.
There is a column of air about a mile high pushing down on you right now. That is about fifteen pounds per square inch at sea level. This means your body is pushing back with the same force. The hot water in the jug heats the air in the jug which pushes against that column of air.
When the air inside the jug cooled, the air contracted, so there was less force exerted against the outside air. The jug got squished until the pressure inside matched the pressure outside.
A different thing happens to divers. As they go down deep into the water, the pressure increases. The air in their blood gets squished smaller. If the diver comes up too quick, they can get the bends. What happens is the little bubbles in their blood suddenly blows up like a balloon. Ow. The bends cause you to bend over in pain.
Another example is flying in an airplane. The air in the plane is pressurized to somewhat match sea level pressure. That is what causes your ears to "pop" when the pressure inside your ear matches the pressure outside. The plane has metal walls and two sets of windows to handle the pressure difference.