In the unfortunate event that you have to put out a fire, knowing how to actually use a fire extinguisher is imperative. Step one is to check if the extinguisher at hand has the proper classification for the immediate fire. Step two is to follow the PASS method detailed below. Some extinguishers differ in their actual operation, so when in doubt refer to their label.
P
Pull the pin. This may require twisting it first, in order to break the zip-tie.
A
Aim the hose (or other attachment) at the base of the fire.
S
Squeeze the handle.
S
Sweep back and forth.
If possible, and safe, keep the extinguisher for recharging or recycling – it is cheaper than buying a replacement and then getting it certified anyways.