Chemical features like 3 dimensional structure and chemical bonding are responsible for diversity in biomolecules although they are made from simple monomers.
In the case of carbohydrates, both starch and glycogen are made up of glucose monomers yet they differ in the functions which they perform in our body. This difference is because of the chemical bonding and the 3 dimensional structure.
Similarly in protein biomolecules, amino acids act as the monomers but they differ in function due to their 3 dimensional structure. Nucleotides are the building blocks of both RNA and DNA. RNA and DNA perform different functions in the body. DNA stores ad transfers genetic information while RNA is responsible for directly coding for amino acids.
Humans get amino acids from protiens in the food we eat. As we digest the food, the enzymes in our stomach and small intestines break down proteins into small amino acids. So technically, we do not make amino acids, we get amino acids from eating food high in protiens.