These are basic shell voicings -- two-note, rootless 'chords' to comp with when a bass player is playing the root and fifth. The red circle represents the unfingered root -- don't play this note -- use it to orient the other essential tones. While the root and fifth remain constant for the minor, major and dominant chords, the seventh and third are what differentiate their character. These are the 'essential tones' -- a shorthand guide to a progression's harmony.
Beyond the first page are other shell voicings included for half-diminished and extended chords. Your shells will generally be two or three note voicings.
I'm teaching myself jazz guitar... these are my notes.