Thermal Grease is a lubricant that fills microscopic gaps between contact surfaces to improve the heat transfer efficiency between components like your CPU and a heat sink. Also known as Thermal Interface Material (TIM), this lubricant is necessary to keep your processor at the optimal temperature, prevent it from damage by poor heat dissipation and prolong its life span.
Typically, thermal paste is sold in small tubes at electronics stores and usually comes with a shovel-like tool to help you apply it. The application process is pretty straightforward – start by wiping off both the heat sink and processor with isopropyl alcohol, seat the processor in its socket on the motherboard, grab your tube of TIM and get to work. Be sure to spread it evenly and remember that you only want to apply a thin layer no larger than the metal die of your processor. If you apply too much, it will start to ooze out and make contact with other parts of the motherboard that can fry them.
Conductive thermal greases, such as those that contain silver or copper, are generally considered the best and tend to be more expensive than non-conductive types. However, they can be risky because they conduct electricity – if you accidentally spill them on your CPU pins or other electrical components, it may cause a short-circuit that will fry the processor and possibly damage other devices. Non-conductive pastes don’t conduct electricity and are safer to use, but they don’t perform as well.