The P-A-S-S technique for fire extinguisher use:
P - Pull the pin. It is there to prevent accidental discharge
A - Aim low at the base of the fire. This is the where the fuel source is
S - Squeeze the lever above the handle. Release to stop the flow(Some extinguishers have a button instead of a lever)
S - Sweep from side to side. Move toward the fire, aiming low at its base. Sweep until all flames are extinguished. Watch for re-igniting. Repeat as necessary. Have site inspected by fire department.
Place any fire extinguisher that has been used on its side on the floor. It will be collected and recharged after the fire scene is secure.