void setup() {
  pinMode(2, OUTPUT);  // Set GPIO2 as output for the LED.
  pinMode(4, INPUT_PULLUP);  // Set GPIO4 as input for the button with pull-up resistor.
}

void loop() {
  int buttonState = digitalRead(4);  // Read the button state.
  
  if (buttonState == LOW) {  // If button is pressed (LOW)
    digitalWrite(2, HIGH);  // Turn LED on.
  } else {
    digitalWrite(2, LOW);  // Turn LED off.
  }
}