Joe already gave you the answer. What he meant by be careful with the volume is, you don't want to overwork your amp (trying to put out more watts than its capable of) and blow your sub.
If you're new to car audio and/or amplifiers let someone who knows set the gains on the amp. Don't turn them up thinking it's a volume control. If you do this you will send a clipped signal to the sub and wind up frying the voice coils on it.