It’s a map of the surface of one part of the brain. Imagine a Star Trek scanning beam going across your head from right to left, about where your ears are. This is a picture of half of that part of the brain (the other part is a left/right mirror image of this picture).

So the cells along the surface of the brain here are connected to the sensory nerves in your body and this is a map showing which body parts are where. So if you move to the top of the brain it is the area where you feel sensation from your abdomen. Go further down the side and you get to arms and then hands, then face. Notice that sensitive areas of your body are much bigger (hands, face) because a lot more brain tissue is devoted to those areas.