If you're shooting with all of your camera's settings on automatic, you're missing out. Your ISO setting -- among others -- can drastically improve your shots when used properly. This video guide from TechQuickie explains what you need to know. In short, tweaking your ISO settings comes in handy when the lighting in your environment is less than ideal, like night shots or situations where the lighting just isn't great at all. As an example, suppose you're taking a family photo, and you have everything dialled in just right, but half of the people in the background of the shot are out of focus. You can bring the f-stop down to increase your depth of field, but now everything is too dark. Increase your ISO, and you keep focus but also bring more light in to the sensor. Similarly, it's useful when you need to get good light in to your camera's sensor, but also need to shoot with high shutter speed, like at a game or another fast-moving event.
Of course, boosting those settings without knowing what you're doing can actually make your photos worse, so take some time to familiarise yourself with how your photos change when you tweak your camera's ISO settings. If you need a quick reference, this graphic explains how ISO, shutter speed and aperture are related.
Camera ISO As Fast As Possible [TechQuickie]