There are two standard laws regarding gas. The Charles law and the Boyles law. They state that, if the pressure is constant, the volume of gas is inversely proportional to the temperature. This means that when the volume will increase, the temperature will decrease. Likewise, at a constant temperature, the pressure is inversely related to the volume. As the volume decreases the pressure of the gas increases.
This helps us figure out the correct relations between the quantities, helping physics figure out the particular behaviors of different gases at a different temperature. It also helps them figure out the changes in the pattern of the gas at different pressures and volumes, unraveling its mysteries.