The STC-1000 is simply an electronic thermostatically controlled switch that's wired into a normal, everyday 2-plug wall outlet to create a "control box".
It senses the temp via its temperature probe that I attach to the side of my LBK. If the temp falls below the set value by 0.5C (the tolerance that I've set), it sends power to whichever plug you've wired for "heat" until the temp goes back up to what you had set, then it turns it off. If the temp goes up to 0.5C higher than the setting, it then turns on the "cold" outlet until it has cooled. If the temp is in the correct range, neither of the outlets have any current to them.
You need to have the freezer or fridge (turned all the way cold) plugged into the "cold" outlet. You also need to have a heat source (like the light bulb inside the paint can) plugged into the "heat" outlet and sitting inside the freezer/fridge.
It's shweet. I can ferment at whatever temp I want at the touch of a few buttons. My next batch, I plan to use Nottingham yeast and will set it for 61F since it's an ale yeast, but reportedly does better at cooler temps.