Dual Pole means it's basically two switches in one package, you can switch two indepenant circuits with one switch. Dual Throw means the switch can be up, center, or down, so given krehmkej's drawing above, up connects Load A with Input, center connects nothing, and down connects Load B with input. As Krehmkej said, the connectors on the switch are usually laid out in a row, so you would put your +12v on the center tap, and one load on each of the top and bottom taps to switch between. In the case of a dual pole, you've got two rows of three taps, and each row works like an independant switch circuit. Here's a URL with some decent pics of switch types:

http://www.kpsec.freeuk.com/components/switch.htm
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