https://www.circuitbasics.com/how-to-control-leds-on-the-arduino/

int redLED = 13;

int greenLED = 2;

void setup() {

  pinMode(redLED, OUTPUT);

  pinMode(greenLED, OUTPUT);

}

void loop() {

  digitalWrite(redLED, HIGH);

  delay(1000);

  digitalWrite(redLED, LOW);   

  delay(1000); 

  digitalWrite(greenLED, HIGH); 

  delay(1000);

  digitalWrite(greenLED, LOW);   

  delay(1000);   

}