Having to use a fire-extinguisher is simple in and of itself; However, the situation that requires it's use can make a simple thing difficult of course. When it come to using a fire-extinguisher just remember the acronym P.A.S.S. to help make sure you use it properly.

P.A.S.S.  stands for Pull Aim Squeeze Sweep. You certainly learned it at one time or another in school. Once learned it is hard to forget, but, a simple review is always good as with anything learned. To operate a fire-extinguisher properly: 

Pull- The first step is to pull the pin ( it usually has the inspection tag attached to it) that prevents the handle from being squeezed. 

Aim- The second step is to aim the spray nozzle, or if attached the hose nozzle, at the fire. Aim low at the base of the fire.

Squeeze- The third step is to squeeze the handle to spray the contents. Remember a standard fire-extinguisher has less than 30 seconds of spray time.

Sweep- The final step is to sweep back and forth as you spray the base of the fire.

A fire extinguisher is only to be used for small fires. As a rule call 911 or have someone call before you attempt to put out a fire. Even if you manage to put out a small fire yourself  call the fire department to have them come check it out.  

As with any stressful situation our thinking becomes a victim of it's own self from the start. Things around us can become unclear, slow moving, or otherwise different. It varies in us all and with the situation, but, there is no escaping that our perceptions become muddled in a stressful situation. Training,  knowledge and experience fortunately help a great deal to compensate.