The temp control coil enables you to control the temperature of your fermenting beer. This can be a crucial component for having a healthy fermentation, as temperature is tied to the amount of activity your yeast will exhibit. Generally, the warmer they are, the faster they work! But you don't necessarily want them to work too fast. If they proliferate too rapidly, often that can be associated with off flavors that you may not have wanted in your beer. Finding the happy medium is key, and the temp coil enables you to hold your beer within a degree.
The key is how you decide to use the coil. You can hook it up to a glycol chiller, an ice bath or (in the case of heating) warm water. Pump whatever liquid you decide through the coil to suit your needs. Many use this in conjunction with a digital controller to control a pump to turn on/off based on the temperature of your beer.
Submersible aquarium pumps are perfect for pumping liquid through our coils.
Quick Connect fittings and 3/8" plastic tubing purchased at home depot are perfect for hooking liquid up to the coil.