Adafruit ESP32-S3 Manual page 132

Analog to Digital Converter (ADC)
An analog-to-digital-converter, or ADC, is the key to reading analog signals and
voltages with a microcontroller. An ADC is a device that reads the voltage of an
analog signal and converts it into a digital, or numeric, value. The microcontroller
can't read analog signals directly, so the analog signal is first converted into a
numeric value by the ADC.
The black line below shows a digital signal over time, and the red line shows the
converted analog signal over the same amount of time.
Once that analog signal has been converted by the ADC, the microcontroller can use
those digital values any way you like!
Potentiometers
A potentiometer is a small variable resistor that you can twist a knob or shaft to
change its resistance. It has three pins. By twisting the knob on the potentiometer you
can change the resistance of the middle pin (called the wiper) to be anywhere within
the range of resistance of the potentiometer.
By wiring the potentiometer to your board in a special way (called a voltage divider)
you can turn the change in resistance into a change in voltage that your board's
analog to digital converter can read.
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