void setup() {
  // Assign digital post 13 to received output signal
  pinMode(13, OUTPUT);
}

void loop() {
  // turn the LED on (send HIGH voltage)
  digitalWrite(LED_BUILTIN, HIGH);  
  // wait for a second. 1 second = 1000
  delay(1000);                      
  // turn the LED off (send LOW voltage)
  digitalWrite(LED_BUILTIN, LOW);
  // wait for a second    
  delay(1000);                  
}