Search google for "peltier module," "TEC" or "thermoelectric module," you will find tons of info on how these work.
They are a heat pump, they move heat energy from one sid of the module to the other. Keep in mind that they can only move as much heat as they can dissapate i.e. a 200+ watt module will need a very efficient or very large heat sink.
They also consume a LOT of energy, that specific one will use up to 20 amps at 12 volt DC, so you need a large expensive power supply to control it.
I have a hooded 24 gallon Aqua Nano and I don't want to drill it. So I was looking for something small and cheap to drop my temp down a couple of degrees or more. It's in the 83 degree range even though the room is air conditioned. I could always use some r.o.-ice and or fan but I thought maybe something else would be better. I didn't want to lose anymore water than necessary.