Answer:
I've never been in a situation where I had to use a fire extinguisher, but at school, they demonstrated it to us.
You have to pull the pin, which will also break the tamper seal. Then you have to aim low, pointing the extinguisher nozzle at the fire. Squeezing the handle will release the white substance that comes out of the extinguisher. While aiming at the fire, just weep the extinguisher side to side at the fire until it appears to be out.
Step-by-step explanation: