Fire extinguishers are specifically designed for incipient stage fires, or fires in the very early stages. Fires in the kitchen and garage can often be controlled by a fire extinguisher (used properly) because people are often present when the fire starts and a extinguisher can be employed early in the fires development. A fire that is not extinguished with a single extinguisher is too big for extinguishers alone and more then likely to they point where you need firefighter's protective clothing to fight it safely... GET OUT and CALL 911! No property is worth a life.
I believe they are primarily designed to give you an
avenue of escape in a serious fire emergency. It takes a 5lb fire extinguisher about 18 sec to completely discharge and the distance and volume diminishes rapidly so you have to approach the fire while sweeping and you have realistically between 7 and 14 sec to provide an avenue of escape and bug out that way.
They are like pepper spray, you have to take the extinguisher and invert it (shake it) five times every month and reread the pressure gauge not only just to see if the needle is still in the green zone but also if it has moved at all. You may also check the hose for obstruction, check the tag to make sure that the extinguisher has been checked last month and up to date, and the mount to make sure that it's properly fastened. And they may work badly outside in windy conditions (like pepper spray).
When you pull the pin make sure you don't squeeze at the same time (just hold the bottle by the lower handle) there are many documented cases of people being killed in a fire found with a charged fire extinguisher in their hands with the handle squeezed completely together and the pin still in place because they were trying to pull the pin while squeezing on the handle.
http://www.youtube.com/watch?v=3G0a-MLneRs(my post is almost a transcript of that video)