You can think about genes as an instruction code and hormones as chemical messages. In terms of genes, most people have 46 chromosomes. Chromosomes are large groups of genes. Two of the chromosomes, the X and the Y, are called sex chromosomes.
Coming up to puberty, they will also need to know a little about the internal organs. Children go through puberty at their own pace; some develop faster than others. Sometimes during puberty it can seem that everyone is growing faster than you, and then you have a growth spurt and catch up. The size and shape of your adult body will have a lot to do with your genes. I know if can be a bit confusing but it will all work out in time. At this stage most children want reassurance that their development is normal.