// declaring integer type variables
const int ledR = 12; //* Red LED connected to pin 12
const int ledA = 10; //* Yellow LED connected to pin 10
const int ledV = 8; //* BLue (I have not a Green LEDs I use a Blue LED ) LED connected to pin 8

//the function is executed only once

void setup() {
  // initialises the led pins as digital outputs
  pinMode(ledR, OUTPUT);
  pinMode(ledA, OUTPUT); 
  pinMode(ledV, OUTPUT);
}
// The loop function runs infinitely

void loop() {
  // red light ON
digitalWrite(ledR, HIGH);
digitalWrite(ledA, LOW);
digitalWrite(ledV, LOW);
delay(1000);

  // yellow light ON
digitalWrite(ledR, LOW);
digitalWrite(ledA, HIGH);
digitalWrite(ledV, LOW);
delay(1000);

  // Green/Blue light ON
digitalWrite(ledR, LOW);
digitalWrite(ledA, LOW);
digitalWrite(ledV, HIGH);
delay(1000);
}