Insulin helps keep blood glucose levels on target by moving glucose from the blood into your body's cells. Your cells then use the glucose for energy. In people who don't have diabetes, the body makes the right amount of insulin on its own. But, when you have diabetes, you and your doctor must decide how much insulin you need throughout the day and night.
This answer is based on source information from the National Institute of Diabetes and Digestive and Kidney Diseases.