In the second lesson, we are explaining how to control some leds by connecting a button as digital sensor:

THIS IS A SOLUTION FOR THE CODE:

void setup() {
  // initialize digital pins 13 and pin 10 as an output, and pin 2 as input
  pinMode(13, OUTPUT);
  pinMode(10, OUTPUT);

pinMode (2, INPUT);
}
void loop() {

if (digitalRead (2) == HIGH){ // condition for the button (HIGH is when pressed)
  digitalWrite(13, HIGH);  
  digitalWrite(10, LOW); // turn the LED 13 on and the LED 10 off                     
 }else {
  digitalWrite(13, LOW);
  digitalWrite(10, HIGH); // alternative ligthning     
}

}