A fire extinguisher is an active device used to extinguish small fires. There are three main types of fire extinguishers: type A, for use on materials like paper, wood, and plastic; type B, for flammable liquids like oil, paint, and chemicals; and type C, for electrical or gas fires. The document provides instructions on how to use an extinguisher using the PASS method: pull the pin, aim the nozzle, squeeze the handle, and sweep from side to side at the base of the fire.