These are used to transfer heat away from the processor. The fan blows cool air past the heat sink which conducts heat from the processor. The heat is dissipated to keep the processor working and to stop it overheating. Without one the processor would overheat and melt. It is attached onto the processor using thermal grease. It is connected to the motherboard by a cable for power. The cooling of the computer can be made even more efficient using water cooling.
