Newbie just tsrating, need help with a sketch

[stiwdio]

@StefanL38

onst byte LedPins[5] = { 8, 9, 10, 11, 12};

unsigned long previousMillis;
int index = 0;
int updown = +1;      // +1 or -1 for going left and right
int buttonstate = 0;


void setup()
{
  for ( auto a : LedPins)
    pinMode( a, OUTPUT);
    
  pinMode(2 , INPUT_PULLUP);  // activates the internal pull-up resistor
}

void loop ()
{
  if (buttonstate == LOW)
  {
    unsigned long currentMillis = millis();

    if ( currentMillis - previousMillis >= 80)
    {
      previousMillis = currentMillis;

      digitalWrite( LedPins[index], LOW);       // turn old led off
      index += updown;
      digitalWrite( LedPins[index], HIGH);      // turn new led on

      if ( index <= 0 || index >= 4)
        updown = -updown;
    }
  }
  else
  {
  }
}

Amazing, thanks Stefan! Great explanation! this will keep me going for a while to figure it out, but thats what's it about working it out
Thank you again!