A partially discharged extinguisher is an empty one. You know how to use your extinguisher. It's too late to read the instructions when the fire is burning. Attend an extinguisher training class if you can. If possible, turn off the electricity first.
P Pull the pin.
A Aim the nozzle at the base of the fire. S Squeeze the handle. S Sweep the nozzle side to side. Before you invest in one of more extinguishers, consider where you need them. Not all extinguishers work on all types of fires.