The term "amino" in amino acid means the amino group (-NH-), and "acid" means the carboxyl group (-CO-), respectively. That is, the name of the amino acid is derived from it's property including both features.
Basically, there are only twenty kinds of amino acids used in natural proteins. Each amino acid consists of two parts, the backbone (-NH-C-CO-) which is common in all amino acids, and the sidechain which is different in each amino acid.
The feature of each amino acid is described below.
The alanine has only one methyl group as it's sidechain. The proline composes a covalent bond between the tip of sidechain and amino group of backbone in it's molecule.