Basic sketch demonstrating a digitalInput with a button

button.ino

int ledPin=13; //Variable to store pin of LED
int buttonPin=3; //Variable to store pin of button
int buttonValue=0; //Variable to store last known value of button state

void setup() {
  // put your setup code here, to run once:
  pinMode(ledPin, OUTPUT); //Setup LED pin for output
  pinMode(buttonPin, INPUT); //Setup button pin for input
}

void loop() {
  // put your main code here, to run repeatedly:
  buttonValue=digitalRead(buttonPin); //Read the value of the button pin
  if(buttonValue==HIGH){ //if the button is open (not pressed)
    digitalWrite(ledPin,LOW); //turn the LED off
  }else{ //otherwise, if the button is closed (pressed)
    digitalWrite(ledPin,HIGH); //turn the LED on
  }
}