Voltage dividers
Vout = Vin × R2 / (R1 + R2): sensors, level shifting and potentiometers.
Two resistors in series split a voltage. With R1 on top (to Vin) and R2 at the bottom (to GND), the middle point is Vout = Vin × R2 / (R1 + R2).
Level shifting a 5 V signal for an ESP32: R1 = 1 kΩ, R2 = 2 kΩ gives 5 × 2 / 3 = 3.33 V.