As you may have learned in your bio
classes, these are the building blocks of protein, which is the major
component of the human muscular system. There are 22 amino acids,
eight to nine of which are 'essential' amino acids and cannot be
produced by the body itself. As a result, these amino acids must
be ingested by through diet and/or supplements.
It has been shown recently that protein breakdown during extended exercise contributes to approximately 10-15% of the substrate energy needs. It has also been recently argued that 'free form' amino acids can be used as performance enhancing (ergogenic) aids. This is still being debated as far as we know.
You don't need to know the technicalities of amino acids, but it is good to know what they are in basic terms.