You have four classes of fires:

Before anyone corrects me, this isn’t all inclusive, there are always exceptions and weird cases, but for the layperson these are what those classes of fires are.

Class A - generally anything that ashes, paper, wood, etc

Class B - chemicals and grease

Class C - electrical fires, like your circuit box

Class D - metal (you probably won’t see this far)

In America there’s a fifth class, Class K, which is kitchen fires. In general this is just a cute way of saying a Class B fire. Most home fire extinguishers are going to be rated for A, B/K, and C. This depends on the agent used to fight the fire.