All amino acids have a carbon atom that has one H, an amino end (-NH₂), and an acid end (-CO₂H). The fourth bond to that central C is to something called a "side group," which can be as little as just an H (in glycine) or big and complicated (like in tryptophan).

The twenty most common amino acids that our bodies use to make protein are listed below.

Note that proline is a little weird - its side group is attached to its amino end. In a protein, prolines tend to make bends or kinks in the chain.