Drag any bead and let go. Tap a bead without dragging to pin it or set it free. The copper rings are pins.
The rule. Each bead is joined to the beads on either side by a spring. A stretched spring pulls its two beads toward each other. A bead adds up the two pulls and speeds up in that direction. That is all. Nothing else in the picture knows about anything but its neighbors.
Listening. The string you see is far too slow to hear. When Listen is on, the same beads follow the same rule, run many times faster, and the up-and-down motion of one bead near the left end goes straight to the speaker. The Pitch slider chooses how much faster: run it twice as fast and you hear it one octave up. A real string moves only a hair’s breadth, so the sound gets your pluck scaled down to that size, same shape. Nothing is recorded. You hear the string.