int ledPin = D2;

void setup() {
  // We want to tell the Argon that we'll use
  // D2 as an output pin.
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // First... On
  digitalWrite(ledPin, HIGH);   // Turn ON the LED pins
  delay(3000);               // Wait for 3000mS = 3 second

  // Now... Off
  digitalWrite(ledPin, LOW);   // Turn OFF the LED pins
  delay(3000);               // Wait for 3000mS = 3 second
  // rinse + repeat

}