Those PSU's replace a standard PSU. So if you have a motherboard that uses a standard PSU, you can use one of those automotive PSU's in its place (assuming the wattage is adequate). Note that laptops don't use standard PSU's, so you can't use, for example an M2-ATX, with a laptop.
As to how they are wired up, each of the PSU's in the mp3car store has downloadable instruction manuals. Download and read, since each one is a little different.