I hope someone can help.

I understand that ohms are a measurement of resistance, I just don't understand how that affects a speaker system. When it comes to impedance, is better to push a lower ohm rating versus a higher rating (i.e. 2 ohms vs 4 ohms)? I would think that it would be better for the speakers, but harder on the amp. Is that true (and I'm making assumptions)? As far as voltage goes, is it better to push more voltage or less (i.e. 12V vs 14.4V)? I would appreciate any input because I am in the dark. And to let you all know I am asking because I am planning on putting a system in my vehicle, and I am not quite sure about the technicalities. Sorry if this is strictly a Home Audio forum and not a Car Audio forum. I have had many questions answered here, so I thought I would give it another try. Thanks all.

Cole J.