Essential amino acids are not synthesized by the body, but need to be obtained from food, or sources outside the body. They are part of the universal genetic code. The genetic code does not make amino acids itself, but uses amino acids created via other processes and incorporates them into proteins. So in other words:
[Metabolism] -> (Non-essential AA) \
..........................................................---> [Genetic code] -> Polypeptides
[Food/Diet/etc.] -> (Essential AA)..../