Chords
A chord is notes stacked in thirds: start on a root, skip a note, land, skip, land. Which size of third you stack, 3 or 4 half steps, is the whole difference between bright, dark, tense, and dreamy. Pick a root and a quality; everything plays.
Build a chord
Every button plays what it selects. The numbers under the notes are the half-step gaps. The chord's fingerprint.
Root
Quality
Why thirds?
Stack every-other note of a scale and the notes ring without crowding. That's a triad: root, third, fifth. The lower third sets the mood (4 half steps = major/bright, 3 = minor/dark); the upper third finishes the shape. Add one more third and you get the 7th chords. Compare the four triad moods on the same root: