With 20 amino acids one makes a distinction between essential amino acids and not essential amino acids. The human organism can produce itself the latter, he must take up the essential amino acids with the food.
With amino acids it concerns already split protein which the body can use where they are used. In the bodybuilding and in the sport generally they are of great importance.
Amino acids must be only split not like protein, but are available to the organism immediately. The body shows above all after a hard training a raised amino acid and protein need. This should be quickly covered by the taking of amino acids and Proteinshakes.