Distance Sensor
You have received HC-SR04 ultrasonic distance sensors. This module, which measures distances using ultrasonic waves, consists of four pins:

VCC: sensor power supply (5V)
Trig: trigger pin
Echo: echo reception pin
GND: ground
Input and Output Voltages
Power supply voltage (VCC): 5V
Output voltage (Echo): 5V
Operation
Triggering: To initiate a measurement, a 10-microsecond signal must be sent to the Trig pin. This triggers the emission of a burst of 8 ultrasonic pulses at 40 kHz.
Reception: The sensor then waits to receive the echo of these pulses. When the echo is detected, the Echo pin goes high.
Time Measurement: The duration for which the Echo pin remains high corresponds to the time taken by the ultrasonic wave to travel to the obstacle and back.
Reminder: The speed of sound in air is approximately 343 m/s.
Connection to the Raspberry Pi
Warning
Since the sensor’s output voltage is 5V, a voltage divider is required to lower this voltage to a level acceptable for the Raspberry Pi’s GPIO pins (3.3V).
Creating the voltage divider:

vertical resistor: 1K ohm, horizontal resistor: 2K ohm
Connect the sensor’s VCC pin to a 5V pin on the Raspberry Pi.
Connect the sensor’s GND pin to a GND pin on the Raspberry Pi.
Connect the sensor’s Trig pin to a GPIO pin on the Raspberry Pi (e.g., GPIO 10).
Connect the sensor’s Echo pin to another GPIO pin on the Raspberry Pi (e.g., GPIO 9).