void setup() {
  pinMode(13, OUTPUT);

  digitalWrite(13, HIGH); // it means on!
  delay(1000); // in 1 second
  digitalWrite(13, LOW); // it means off!
  delay(1000); // in 1 second
  digitalWrite(13, HIGH); // it means on!
  delay(1000); // in 1 second
  digitalWrite(13, LOW); // it means off!
  delay(1000); // in 1 second
  digitalWrite(13, HIGH); // it means on!
  delay(1000); // in 1 second
  digitalWrite(13, LOW); // it means off!
  delay(1000); // in 1 second
}

void loop() {
  // put your main code here, to run repeatedly:

}