The ISO for beginners look like a devil of this science. But it is not. ISO abbreviated for International Standards Organization is a standard for the camera sensor sensitivity. On a camera one can find ISO 100,200,400,800,1600 up to 6400 as the ISO settings. ISO gives one the sensitivity of the camera sensor. If the light around is sufficient for the photo capture, then least ISO i.e. ISO 100 is selected. As the Light level around goes on decreasing the ISO value goes on increasing.
  So take your camera and try changing the ISO settings of the camera and take the perfect click.