#define led 2                //Set the pin controlling the LED to pin #2

void setup() {  
  pinMode(led, OUTPUT);      //Set the LED to be an output
}

void loop() {
  digitalWrite(led, HIGH);  //Turn the LED on

  delay(1000);              //Wait 1 second, remember: delay function uses miliseconds
                            //1s = 1000ms
                            
  digitalWrite(led, LOW);   //Turn the LED off

  delay(1000);              //Wait 1 second

}