The main view in this visualization shows a small circle for each residue, located by the N chemical shift on the Y axis and the H chemical shift on the X axis. For the selected amino acid(s), all of the appropriate circles are filled in with a red dot.
The left view shows the three-letter amino acid abbreviations, along with the number of occurrences of each amino acid in the molecule. The cursor selects the amino acid(s) to highlight in the main view.