It's called genetics. DNA of both parents contain genes that are passed on to the children. These are traits, physical characteristics you see in people. Short, average, tall. Hair color, eye color, shape of the face, shape of the nose, etc.
Each parent has their genotypes and phenotypes also alleles. Which has the dominant trait and recessive trait. In the body we have specific numbers of chromosomes and different alleles. So that's why you look like your parents(unless your adopted:/) because they give part of their DNA and in alleles there are 2 parts, 1 from your mom and 1 from your dad. You get one from each and get your own set of genes. Like LL-long legs, which is dominant(L) and (l) being short(which is recessive. Ll would be long but ll would be short.