Where you pluck decides which harmonics ring. Park the plectrum anywhere between bridge and midpoint: each bar shows how much of that harmonic's possible strength your pluck spot feeds it, the thin lines are the harmonics themselves rising and falling, and the string on top is their sum. Pluck, and it pinches into a triangle right under the plectrum. Add the blue touch finger and only the harmonics with a node under it survive (a node is a point where that harmonic doesn't move at all). That's the natural-harmonics trick, on screen: try it over the 12th, 7th and 5th frets. The switch above the string shows the harmonics apart, together, or not at all. The Try row plays the four guided plucks from the Foundation guide.
Handed to you by Foundation · Harmonics. The law behind the plectrum: the strength of harmonic n is sin(nπp)/n².
Read it like your guitar. Near the bridge the high harmonics come through strong: the bright, cutting tone of picking close to the saddle. Toward the midpoint (the 12th fret) they fall away and the sound rounds off, the way it does when you pick over the neck. The bars aren't a simulation of that trade; they are it: your picking hand has been running this law all along. And the touch finger is how harmonics are actually played: rest it over the 12th, 7th or 5th fret and pluck.
The note names on the bars are the stack from Foundation's harmonic table: the root, its octaves, the fifth, the major third. That's the chord your string builds for you.