Ohms are the little people inside a speaker. when they get fed they push and pull on your speaker cone from the inside to make sound. They can push really fast to get high notes and really slow to get low notes. (some ohms can push slower and faster than others) Usually there are small families of 4 or large families of 8. They get hungry so you have to feed them with your amp. The amp has to pump juice into your cabinet to feed the little ohms.
Their juice is called watts. The big families have more kids so they need more juice (watts) to feed them. The little families need less juice to make the same amount of noise.
Now when two families live side by side most of them get together and goof off so it seems like there are fewer ohms to feed. so instead of two families of eight needing twice the juice (watts) you only need to feed four of them and they do more work to make up for the twelve that are goofing off.
So I hope this helps. the important thing to remember is that more is less. 8+8 = 4. nuff said.
Now really, ohms measure how much resistance your speaker has (oops impedance really) and when you hook up two in parallel, through a daisy chain on the cab or connect with a Y cable, you get half the impedance. think of it as two paths to get to ground instead of one. So if you had a perfect amp, it would be able to give you twice the power. But it has limits, so usually it is less than twice.
When you hook up more than two 8 ohm speakers together you get less than 4 ohms and some amps don't like this, so they try to send out more current then they are capable of and get hot and eventually blow up. (there are other factors too)
Make sure you don't get too many of those ohm people goofing off.
OTOH, if you connect too big of an amp to your speaker it will put too much power into the speaker and the voice coil will heat up causing it to melt or "blow" (kinda like the transmission in my van did yesterday). Clipping your amp is bad too - the speaker sees it as a really high power signal (hard to explain, but it's like hooking up a huge battery to your speaker - it causes the cone to stop moving momentarily and all that juice drowns the little ohms - then they can't push the speaker).
So, laugh, cry or flame me for being confusing. But don't hook up too many speakers. Ohms have rights too you know.
Who's explanation do you like better?