Answer:
According to the Ideal Gas Law, first stated by Emile Clapeyron as a combination of the existing Boyle's Law and Charle's Law, pressure of a gas (air is a mixture of gases) can be increased by either decreasing the volume, increasing the amount of gas particles in the compartment, or by increasing the temperature. Air compression is done through the first option of forcibly decreasing the volume of the container. While there are many types of gas compressors, the most commonly available method (reciprocating compressor) is to drive air into a compartment then use pistons to shrink the volume of the gas.