Stalling an aircraft is similar to stalling a car only to the degree that forward motion has stopped or is reduced to a dangerous level. When a car stalls, you coast over to the side of the road and park. In an airplane this option isn't available. Wouldn't it be nice if you could coast over to the nearest cloud, get out and lift the hood for a look see.
When air flow over the wings is insufficient to create enough lift to support the weight of the aircraft you have placed the aircraft into a "Stall" condition. Does this always mean your engine has failed and your about to crash back to mother earth, not necessarily.
If you are attempting to climb to a higher altitude and your climb is steeper then the amount of thrust developed by the engine can manage, your airspeed will drop off. At the point that lift is diminished beyond limits, you stall. Lift can be affected by many things, ice buildup on the wings, wind conditions, engine performance, even excessive weight.
A malfunction of the landing gear will create drag and possibly lead to a stall. A control surface issue might be the culprit slowing the aircraft, the reasons for a stall condition are many.
When you find yourself in a stall in most planes you will experience an audible warning, it could be a warning buzzer, or even a voice announcement repeating "Stall, Stall". The yoke or control stick will have a shaker that vibrates the control as a warning. When you go into a stall you will know it.
If a stall happens at very low altitude you have a serious problem. The one thing mandatory to recovering from a stall is altitude. The higher up you are, the more time you have available to correct the situation.
When at altitude, all that may be required is to ease off on your rate of climb to increase your air speed. If you have allowed your stall to reach the point where there is little or no airspeed, a nose down attitude may be used to increase airspeed and regain control. While dropping with your nose down, air is rushing over the wing surfaces and again creating lift. Once airspeed is high enough you can gradually pull back on the controls and level out being careful to maintain proper air speed.
Obviously this eats up a lot of altitude fairly quickly, fine if your at 10,000 ft, but if it happens at takeoff your likely to end up in the trees before you're able to recover.
The worst type of stall would be the flat spin. Considered in some instances one that is unrecoverable. The aircraft is spinning on its horizontal plane while dropping out of the sky. Making it very difficult to get into the nose down position.
Using the rudder and ailerons to counteract the spin until you can get the nose to drop may bring it around, but again altitude means everything.
In the event of engine failure, the ability of a plane to glide will determine how susceptible it is to a stall. Small planes can stay airborne for a long time gliding along relying on the lift of the wing and airspeed to keep them up.
A jet fighter on the other hand has the glide characteristics of a rock and will stall quite readily, falling immediately from the sky.
As you can see, a stall isn't always a death sentence, knowing how to recover from a stall is mandatory and is also a requirement to obtain your pilots license.