L = line thats the hot wire that comes from your circuit breaker.
N = neutral thats the other wire
upsidedown christmas tree = ground.
ok, to make it simple, assuming you are in the USA, and have a 115 volt plug that is fairly modern, that you would plug in the tv or a toaster, etc.
The smaller of the two slots is the line. The slightly larger slot is Neutral. The round one is ground.
Usually, the Line wire is black, the Neutral wire is always white, and the ground is always green. (wiring from china, ground may be yellow, with a little green on it)
Take your volt meter, set to AC (~) and plug one wire into the round hole (ground) of your household plug. Plug the other in the smaller slot, and you should read 115 volts. Take the wire out of the smaller slot and put it into the larger one, and your volt meter will read 0 between neutral and ground. plug the two wires into the two slots and you will read 115 volts. If you read 57 volts between ground and either of the slots, that means you have a step down transformer that don't have the ground hooked properly to it.
Sometimes the wrong person wires a house or building and gets the wiring messed up.
Good Luck Bro