NEED SOME HELP

Hello everyone I'm new to this I just wondering if you guys can help me out. I'm trying to build a circuit but I don't know were to begin or what components I should use. I need to the circuit to deliver current to a TE modules which will be heating up a liquid once the liquid has reached the desired temp the circuit needs to cut off the current or reverse to the current to cool the TE modules if it exceeds the desired temp....if anyone can help me i would really appreciate it. Thanks