What is the thumb rule for fire extinguishers?

Excuse me, could you elaborate on the thumb rule for fire extinguishers? I'm interested in knowing the general principle or guideline that one should follow when dealing with fire extinguishers, perhaps in terms of safety precautions, usage, or even choosing the right type for different types of fires. I understand that this rule could be crucial in ensuring the safety of individuals and property in case of a fire emergency. Could you please explain it in simple terms?