What does the ISO setting on a digital camera actually do?

If you are new to photography, there might be tons of questions in your mind related to what every button and setting  on your camera is meant for. One such setting that you don't know anything about is the ISO. It is represented by some numbers like 100, 200, 400....3200 etc. You may wonder what do these numbers represent?  What happens when I select a higher or a lower number? How does it affect my picture etc. and the question are countless.

Below is some explanation about ISO setting and what does it do. Hope it helps you at least a little to get an idea as to what it is and what it is meant for.

ISO represents the measure of a digital camera sensor’s sensitivity to light. It is measured in numbers like 100, 200, 400, 800, 1600 etc. The lower the number the lower the sensitivity. Lower ISO ensures fine pictures and high ISO will give you a grainy picture. When you raise the ISO setting you also raise the noise level. Noise will appear in the photo as a grainy appearance in darker areas of the photo. Higher ISO settings are generally used in darker situations to get faster shutter speeds. A 100 ISO is generally accepted as ‘normal’ and will give you lovely crisp shots.

The changes in ISO are generally made to help with lighting conditions. A higher ISO (represented by a higher number) will allow us to shoot in lower lighting conditions without having to alter the shutter speed and aperture settings. However, it should be noted that a higher ISO setting will cause there to be more grain (known as "noise" in digital photography) and image deterioration can become obvious.