This sketch reads the state of a button (pressed or unpressed) and turns on an LED when the button is pressed.

button.ino

/*
    Pushbutton sketch a switch connected to pin 2 lights the LED on pin 13
*/

const int ledPin = 13;   // choose the pin for the LED
const int inputPin = 2;  // choose the input pin (for a						 
                         // pushbutton)					

void setup() {	
  pinMode(ledPin, OUTPUT); // declare LED as output						 
                           
  pinMode(inputPin, INPUT); // declare pushbutton as input	
  }

void loop(){	
  int val = digitalRead(inputPin); // read input value
	
  if (val == HIGH)
	{
		digitalWrite(ledPin,HIGH);
	} else
	{
  		digitalWrite(ledPin,LOW); 
	}
}