Copy this Code into Arduino:

// constants won't change
const int TRIG_PIN = 14;  // Arduino pin connected to Ultrasonic Sensor's TRIG pin
const int ECHO_PIN = 13;  // Arduino pin connected to Ultrasonic Sensor's ECHO pin
const int LED_PIN  = 16;  // Arduino pin connected to LED's pin
const int BUZZER_PIN = 2; const int MIN_DISTANCE = 10;  // Minimum distance for LED on (cm)
const int MAX_DISTANCE = 50;  // Maximum distance for LED on (cm)

long duration;
float duration_us, distance_cm;

void setup() {
  Serial.begin(9600);  // Initialize serial port
  pinMode(TRIG_PIN, OUTPUT);  // Set TRIG_PIN as output
  pinMode(ECHO_PIN, INPUT);   // Set ECHO_PIN as input
  pinMode(LED_PIN, OUTPUT);   // Set LED_PIN as output
  pinMode(BUZZER_PIN, OUTPUT); // Set BUZZER_PIN as output
}

void loop() {
  // Send a 10-microsecond pulse to TRIG pin to start the measurement
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure the duration of the pulse received by ECHO pin
  duration_us = pulseIn(ECHO_PIN, HIGH);

  // Calculate the distance in cm (speed of sound is 0.034 cm/us)
  distance_cm = (duration_us * 0.034) / 2; // Divide by 2 because pulse travels to object and back

  // Check if the distance is within the defined range
  if (distance_cm >= MIN_DISTANCE && distance_cm <= MAX_DISTANCE) {
    digitalWrite(LED_PIN, HIGH);      // Turn on LED
    tone(BUZZER_PIN, 1000);           // Generate tone (1 kHz frequency for active buzzer)
  } else {
    digitalWrite(LED_PIN, LOW);       // Turn off LED
    noTone(BUZZER_PIN);               // Stop buzzer sound
  }

  // Print the distance to Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance_cm);
  Serial.println(" cm");

  delay(500);  // Wait for 500 ms before taking another measurement
}

Download this file and 3D print it

https://www.youtube.com/watch?v=HynLoCtUVtU

Put the machine you just build from the tutorial into the box you 3d printed and plug it into a computer capable of running arduino then download the code you pasted into ardiuno onto the machine.