ISO is one of the most important camera settings, you will significantly improve not just the quality of your photos, but also the variety of them too by making good use of the ISO setting.
Years ago, in the days of film, now being lost in the midst of time, the film manufacturers used to print a number on the side of the box. This number represented the speed of the film, that is, how sensitive the film was to light, and the higher the number, the more sensitive was the film to light. Using a higher ASA film made it much easier to take photos in low light or to take fast moving subjects, i.e sports or birds in flight. The problem was, especially in the early days of film, the higher the ISO, the more 'grain' was introduced to the negative and consequently the prints.
In this digital age, the term ASA has been replaced with ISO, and 'grain' is now referred to as 'noise'. With film, yo were locked into the ASA for the whole roll of film, the only way of varying the ASA while shooting was to carry another camera body loaded with a different film. How times have changed, we are now able to vary the ISO on a frame by frame basis, plus in my opinion the quality of high ISO images is now better than it was with film.