Diabetes mellitus is a metabolic disorder characterized by high blood glucose caused by issues with insulin secretion or action. There are three main types: type 1, type 2, and gestational diabetes. Diabetes occurs when the pancreas does not produce enough insulin or the body does not respond properly to insulin. Treatment involves lifestyle changes like diet and exercise as well as medication like insulin or other drugs. Management of diabetes is important to prevent complications and involves self-care activities and monitoring of blood glucose and weight.