The document discusses standing waves on a string that is 1 meter long and fixed at both ends. It explains that when the string is plucked at its fourth harmonic, nodes will occur at quarter, half, and three-quarter distances along the string. Specifically, the nodes will be located at 0.25 meters, 0.5 meters, and 0.75 meters. At these node locations, one can press down on the string without affecting the amplitude of the standing wave.