They are called plate chillers because they're essentially a stack of plates, connected to the in and out ports, forming flat thin channels for the water and wort to flow in opposite directions. The outside pair of plates on each side form the two outermost channels, and those you want to have water running through, which would then put the outermost wort channels under those two outside cooling channels. From there working to the center the channels simply alternate between wort and water on both sides.
You should be able to figure out which pair of ports are connected to the outside channels by running some hot water through one set. If the outside plates immediately get hot, you've found the cooling ports. If not, you're hooked up to the wort ports...
Cheers!
