The skull is the large bone in the head of vertebrates. Humans are also among these animals. For experts, it is not a single bone: A skull consists of 22 to 30 individual parts, depending on how you count. They are fused together, but you can clearly see the sutures.
Only one bone on the skull is movable, the lower jaw. The skull's most important job is to protect the brain from injury. The brain also needs a shell because it is very soft and is a particularly important organ without which one cannot live.
The skulls of mammals, birds, fish, reptiles and amphibians differ from each other, but they are still quite similar. Among the mammals, humans have a special feature: the spinal column does not start at the back of the skull, but at the bottom. That is why the hole for the thick nerve cord is not at the back, but at the bottom. This enables humans to walk upright.
In a baby, the bones in the face are properly fused together, but at the back of the head they are still very mobile. At the top of the head, the skull even has a really big hole that is only covered by skin. This is called the "fontanelle". You can see it well and feel it carefully. But you must never press on it, otherwise you press directly on the brain. During birth, these parts of the skull are pressed together, which makes the head a little smaller and thus makes the birth easier. So this is a completely natural process.
However, nothing unpleasant should happen to the skull later on, because the brain is also injured very quickly. This can have serious consequences. That is why you should always wear a helmet as protection when cycling or doing certain sports such as kickboarding or rollerblading.