First of all how do you know you need one? Hmmmm...
Ok how they work:
the pump is inside the transmission, if you have the right radiator you already have one built into it. The fluid from the transmission is pumped through the lines into a separate chamber and back into the transmission. We you add another cooler you are adding more surface area to dissipate the heat.
How to install (much more involved than this explanation):
You need to mount it where it will get good air flow, then you split one of the lines going from the transmission to the radiator, attach the rubber lines that come in the kit, and your done…now the fluid flows out of the transmission, into the radiator, then into your auxiliary cooler, and back into the transmission….
Hope this helps….and as I mentioned this is a very oversimplified explanation….so if you need more info ask.