//BTN LED INPUT_PULLUP

int LED_PIN     = 5;
int BTN_YELLOW  = 6;
int BTN_RED     = 7;
void setup()
{
  pinMode(LED_PIN,    OUTPUT);
  pinMode(BTN_YELLOW, INPUT_PULLUP); //PULLUP makes the pin HIGH
  pinMode(BTN_RED,    INPUT_PULLUP);
}

void loop()
{
  //with PULLUP when button pressed it will go LOW
  //check both buttons are pressed, then blink the LED
  if ((digitalRead(BTN_YELLOW) == LOW) && (digitalRead(BTN_RED) == LOW)) 
  {
    digitalWrite(LED_PIN, HIGH);
    delay(1000);
    digitalWrite(LED_PIN, LOW);
    delay(1000);
  }
  else
  {
    digitalWrite(LED_PIN, LOW);
  }
}