A Google of wiring+speakers+series+parallel+effect produces 43,500 hits.
Here's a sample from:
http://colomar.com/Shavano/speaker.html
By the way, when you hook things up in parallel, the power thru the speakers is shared equally. This says that you can't casually put unlike speakers in parallel. For example, a 15 inch woofer and 6 inch midrange speaker should not be wired in parallel - the 6 inch midrange is apt to be destroyed once you crank the volume up. What does work is taking like speakers (ones that are rated for the same power handling capacity) and wiring them in parallel. We won't get into crossover networks (which is one way of powering different function speakers within the same cabinet) at this time.
When you wire in series, the load is split across the speakers based on resistance, but because the total resistance is higher, the actual power that each speaker absorbs is less. If you were to wire 2 40watt speakers in series, you end up with a power handling capability of 80 watts. Typically all of the speakers in a cabinet are the same resistance (8 ohms, for example), however you can mix them. Keep in mind that those with lower resistance will absorb more power - they must be able to handle it or else you can burn out a voice coil.
Only 43,499 to go!