A piezoelectric speaker (sometimes colloquially called a "pizo") or buzzer is a loudspeaker that uses the piezoelectric effect for generating sound. The initial mechanical motion is created by applying a voltage to a piezoelectric material, and this motion is typically converted into audible sound using diaphragms and resonators. Source: Wiki

Here we are toggling a bit port ... one pin on the MCU chip/module and the frequencey we toggle that pin is how we create tones in the speaker.

A math assignment might be calculating how many toggles/cycles of the PIN it takes for each note of the scale.

click to magnify the image

With a Frequency Counter or Oscilloscope you can see the exact output!