This code means your cylinder #2 is misfiring.
It could be one of the following: -bad spark plug/spark plug wire/ignition module/coil
-bad fuel injector
-poor compression (maybe a burned valve)
You could also have too much air getting to that cylinder; maybe a bad EGR valve. With a scanner check your short and long term fuel trim. If you get over 10, rev your engine at 2000 rpm for a little bit and check your short term fuel trim. If it drops you have a vacuum leak; if it doesn't drop, you have a fuel delivery problem (likely a dirty fuel injector).
Try swapping the spark plug and wire from cylinder #2 to another one and see if you still have the same error code. If you do, your spark plug and wire are okay, the problem lies somewhere else. However, if you get a different misfire code (let's say you swap the plug and wire with cylinder #3 and you get a p0303 code) then you know you need new plugs and wires (I would replace all the plugs and wires in this case because if one fails the others are likely to fail soon as well).
You can also do a compression test on cylinder #2; low compression would likely confirm a burned valve.