Amino acids are rightly called "building blocks of life", because our body builds all essential proteins from them. Amino acids are divided into proteinogenic (e.g. arginine) and non-proteinogenic amino acids (e.g. ornithine).
L-amino acids are of great importance in biochemistry because they are the building elements of peptides and proteins. Depending on their length, amino acid chains are called peptides or proteins. Amino acid chains with a length of less than about 100 amino acids are usually still called peptides, only from a larger chain length are called proteins.
Proteins taken as food are broken down into L-amino acids during digestion. They are further utilised in the liver. They are either used for protein biosynthesis or broken down.
So far, 23 proteinogenic amino acids are known and 400 non-proteinogenic, naturally occurring amino acids that have biological functions. The number of synthetically produced amino acids and those theoretically possible is considerably larger.
By the way, amino acids do not only exist on earth, but also on comets, meteorites and even in gas clouds.