How does air exert pressure?
Consider the molecules of a gas moving at random in a container, as shown below.
The molecules are continually colliding with each other and with the walls of the container. When a molecule collides with the wall, they exert small force on the wall The pressure exerted by the gas is due to the sum of all these collision forces.The more particles that hit the walls, the higher the pressure.
If a gas is heated up, its particles move around more quickly. They hit the walls of their container harder and more often. This increases the pressure. Sometimes the pressure gets so great that the container bursts.
This is why balloons and tyyres burst if you blow them up too much. It's also why deodorant spray cans carry warning signs to tell you not to leave them in the sunshine. If they get too hot they explode.