What do you do when the heater fan does not work?

1st check fuse , then or resistor and then blower motor itself resistor is usually under hood right by blower motor or on the ducking it self google images resistor for your kind of car so you know what your looking for power should be going into it when your heater is on and coming out the other side the higher the setting the more power coming out the other side going to blower motor