Pulse Width Modulation (PWM) is a technique for getting analog results with digital means. Digital control is used to create a square wave, a signal switched between ON and OFF. If you repeat this on/off pattern fast enough with a LED for example, the result is as if the signal is a steady voltage between 0 and VCC controlling the brightness of the LED.
A piezo buzzer is a small device that converts electrical signals into sound waves. Unlike traditional speakers, piezo buzzers operate on the piezoelectric effect. When a voltage is applied, the buzzer's piezoelectric crystal deforms, producing sound waves. This simplicity makes piezo buzzers cost-effective, lightweight, and ideal for applications where the space is limited.