The "something" I chose to demonstrate Guy-Lussac's law of P1/T1=P2/T2 - or stating that pressure and temperature in gases have a direct relationship - was my own pressure cooker.
A pressure cooker is basically a pot with a lid that can be sealed. It also has a switch that controls how much pressure is in the cooker. It works by capturing steam which raises the pressure. This pressure increases the boiling point of the water. Normally, water boils at around 100 degrees Celsius. However, the pressure cooker raises the temperature to about 120 degrees Celsuis, which drops the amount of time it takes to cook the food.
This works according to Guy-Lussac's law. As the pressure in the cooker rises due to the steam from the water, the temperature of the cooker also rises. What is happening at a smaller scale is that since the volume of the cooker is set and can't be moved, the particles now have more pressure to hit the walls of the cooker with but the same amount of space to hit. Since the pressure also raises the temperature, the particles also hit the same amount of space with more pressure and more speed.