There is two types of cooling in a computer, liquid cooling or fan cooling. Liquid cooling works by pouring water or coolant into a tank or reservoir, which is connected to a pump unit. The pump pushes the fluid out through a network of pipes to a 'block' of highly conductive metal, usually made from copper or aluminium. This 'block' has one finely milled side, which is clamped on top of the CPU or GPU and has narrow channels running throught its core, the water flows through these channels, absorbing the heat from the rest of the material and exits the CPU or GPU block on its way a radiator. When the water reahces the radiator, it is pushed through a network of even narrower channels, which are cooled down by having air blown over them by fans, the water then flows back to the reservoir and repeats this process. Fan cooling is . The main differences between Liquid cooling and Fan cooling, is that water cooling cools your computer down much more than fan cooling but isnt necessary unless your computer heats up a lot or over heats with normal fan cooling, this problem can also be fixed by getting a case that includes more fans and has a good venting system to cool yor computer down more, but liquid cooling is more garunteed for cooling down your computer than this option. The other main difference is price, because there is more components to a water cooler than fan cooling, so more things that are also more expensive then fans means more total price.