I have been reading around here a lot and I keep seeing people talk about crossovers. Is it something that comes with all speakers that helps with sound quality?
crossovers allows the user to isolates certain frequencies to maximize the performance of a speaker. There are two types of crossovers a passive and active. You should definatley read the audio101 section to learn more.
basically its to help your sound, no one speaker is well equipped to run the full sound spectrum, a crossover isolates frequencies to better match your speekers for instance tweeters will run the higher frequencies 2khz-20khz subs run 60 hz and below et cetera if you run full signal to all your speakers it will not be optimum and may cause damage