Amino acids are naturally occurring compounds possessing two functional groups, an amine (-NH2) and a carboxyl (-COOH), as well as a sidechain (R) that is unique to each molecule. Over 500 amino acids have been classified, although only 20 are coded for in the genome. Amino acids are to the genetic language what letters are to the linguistic one - they are the alphabet of DNA. Every 3 nucleotides (the building blocks of DNA) codes for 1 amino acid, and many amino acids are strung together to form a protein. See below for videos discussing amino acids further and a chart of the 20 essential amino acids.
See here for more on proteins.