You try to start your car, but you flood the engine. Relax -- usually a flooded engine can be started.
A "flooded engine" simply has too much gas in its cylinders, so the spark plugs can't ignite the fuel-air mix. It can happen for a variety of reasons -- most commonly, because you pumped the accelerator pedal too many times when your engine hadn't been started for a while. The trick is to get all the air you can into the cylinders to lean out the overly rich air-fuel mixture.
Press the accelerator all the way to the floor. Don't pump it. Just floor it and hold it there. This opens the choke farther than usual and lets more air in. With the pedal to the floor, crank the engine for 15 seconds. If the engine tries to start, don't pump the pedal: Keep it to the floor for a bit, to let the engine "clean itself out." Release the pedal after the engine starts running smoothly and at a high rpm (revolutions per minute). Letting the engine race for a while won't do it any good -- in fact, it can damage it.
If the car doesn't start after 15 seconds, stop and wait a couple of minutes, to let the starter motor cool down, and crank again. If you just continue cranking past 15 seconds until the engine starts or the battery dies, you may overheat or damage the starter.
If your leg can stand it, don't release the accelerator pedal while you wait, leave it pressed to the floor. Releasing the pedal and then depressing it again will just shoot another spurt of gas into the intake manifold, and you have too much gas in there already.
After a couple of minutes crank again for 15 seconds. This will usually do it. If after two 15-second cranking periods the engine doesn't even try to start, you may have some other problem and should check or have someone check the engine further.