int button = 5, relay  = 6;

void setup()
{
  pinMode(button, INPUT_PULLUP);
  pinMode(relay, OUTPUT);
}

void loop()
{
  int buttonState = digitalRead(button);
  if (buttonState == LOW)
  {
    digitalWrite(relay, HIGH);
  }
  else if (buttonState == HIGH)
  {
    digitalWrite(relay, LOW);
  }
}