The body changes sugar into glucose, it is found in the blood of ones body and keeps at a constant level. It is produced by the pancreas, a gland located behind the stomach. The pancreas produces insulin; but in a diabetic, lacks insulin and the blood sugar rises above normal (prevents the body from using sugar normally). Glucose is a form of energy. Insulin is needed to keep the glucose at a normal level.
The diabetic cannot produce enough insulin on their own. Some diabetics produce no insulin and have to inject insulin into themselves.