// set up pins
int btn = 7;
int led = 8;

void setup()
{
  // setup pinModes
  // LED is OUTPUT
  pinMode(led, OUTPUT);
  // Button is INPUT
  pinMode(btn, INPUT);
}

void loop()
{
  // check if the button is pressed (ON)
  if(digitalRead(btn) == HIGH)
  {
    // Button is pressed
    // switch on the LED
    digitalWrite(led, HIGH);
  }
  else
  {
    // Button is not pressed
    // switch off the LED
    digitalWrite(led, LOW);
  }
}