The only thing I'd add to Scott's post is that, for each increase in the "order", the crossover slope increases by 6 db/octave. In other words, a 1st order crossover has a 6 db/octave slope, a 2nd order crossover has a 12db/octave slope, etc.
That means that, for a 1st-order 1kHz crossover, at 2kHz (for low-pass), or at 500Hz (for high-pass), the signal will be 6db lower than at the crossover point (typically defined as the -3db point, because both drivers contribute to the sound where they overlap)
