Please take a closer look to your digital camera, then you will find the features of ISO or ASA on analog cameras. ISO settings will affect the outcome of your photos. ISO is one of the important things in photography. What is ISO? ISO is a measure of the level of the camera sensor sensitivity to light. The higher the ISO setting, so the more sensitive we to the sensor light.
To get clear information about the ISO setting on our camera (ASA in the case of photographic film), so we think about a bee community. An ISO is a worker bee. If I set the camera at ISO 100, which means I have 100 worker bees. And if my camera set at ISO 200 means I have 200 worker bees.
Is the duty of every worker bees collect the light coming through the lens of a camera and make a picture? If we use the identical lens and aperture together we set at f/3.5, but I set the ISO at 200 while your 100 (think again of worker bees), the picture had who would finish faster?
When we increase the ISO setting from 100 to 200 (the aperture is always a constant - we lock the aperture at f/3.5 or through Aperture Priority mode - A or Av), we shorten the time needed in making a photo on our camera sensor by half ( 2 times faster), shutter speed of 1/125 to 1/250 sec.
As we add more ISO to 400, we cut back on the manufacture of the photo until half: 1/500 sec. whenever exposure shortens as much as half, we call exposure increase by 1 stop. You can try this in the case of aperture, shutter speed we try to set constant at 1/125 (or via the Shutter Priority mode - S or Tv), and change-change your ISO setting in multiples of 2; missal from 100 to 200 to 400 ... etc., look at the amount of change your aperture.
ISO setting had to be adjusted to the conditions at the time of shooting, the light conditions, indoors, or shooting scenery (landscape), and so on. Perform exercises in a variety of shooting conditions, so you better understand the use of the camera as possible.