You get your DNA from your mother and father. This contains lots of instructions to your cells on how to divide and which other cells they should stick to.
Your environment also determines how you grow, both before you are born and throughout your life. If you don’t get enough nutrition or oxygen you won’t grow properly. Current adults in European countries are taller than their parents on average. This is probably because they were fed better as children.
We don’t really understand how our bodies grow into the exact shapes they do, or how they repair themselves after injury. I think it’s amazing that fingerprints can grow back after we’ve cut our skin.
Scientific experiments have shown that the same genes control growth in lots of different types of living things, although their effects may be completely different in the different species.
That’s a great answer by Jonathan! Your DNA is arranged into “genes”. A gene is like a pattern which the human cell follows to make the proteins that carry out all the cells’ functions. Humans have around 23,000 genes. We still don’t know what they all do, or how they all work together to “make” the human body.
Since Jonathan & Sam have answered this so well I’m going to tell you what the body is made out of:
Most of the human body is made up of water, H2O, with cells consisting of 65-90% water by weight. Therefore, it isn’t surprising that most of a human body’s mass is oxygen. Carbon, the basic unit for organic molecules, comes in second. 99% of the mass of the human body is made up of just six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.