Amino acids are the monomers of proteins. The basic parts of an amino acid are an amine group, a carboxylic group, and a side chain, all attached to an alpha-carbon (central carbon).
The bond between two amino acids is called a peptide bond.
There are only 20 R-groups, and therefore only 20 kinds of amino acids found in nature, 8 of which that can be produced by humans. The rest we have to obtain by eating stuff, and these are called essential amino acids.
Surprisingly, the number of combinations of amino acids is almost endless.