My fridge is quite an old-fashioned design. These days you are far more likely to have a fridge-freezer. But this design has a small freezer box incorporated in the main fridge. It is at the top because it is good at chilling the air. This makes the air contract and become more dense. Dense air sinks and as it falls, it chills the food on the shelves below. This is what a fridge is supposed to do.
The back of a fridge is made of twisted black metal. This is because it needs to get rid of the heat that is removed from the contents of the fridge (to cool something you need to take heat away from it). It is black because black is a good emitter of heat radiation. It gets rid of heat easily as infra-red. It is twisted to give a big surface area. Infra-red leaves from the surface and the bigger the surface the more can leave at once. Oh, and if you touch the back of a fridge you'll notice that it is warm.
