The carbohydrates in the foods we eat are broken down into sugars (glucose) which enter the bloodstream. The body releases insulin in response to the blood glucose. Insulin opens up the cells to allow the glucose to enter, thus providing nutrients and energy to the body.
In diabetics, however, there's not enough insulin or else the cell receptors don't respond as they normally would. In either case, the glucose cannot enter the cells.
Due to this impaired function in the body, diabetics need to control their blood sugar levels through a combination of things. First, a healthy and nutritious diet with "diabetes-friendly" foods (see the glycemic index for one way of choosing foods) and regular meal times will help. Second, if you're overweight, a weight loss of even just 10 or l5 pounds can help because it reduces insulin resistance. Third, a regular exercise program (with both aerobic and resistance training) can help you feel better while also improving your body's response to insulin; control cholesterol and high blood pressure; and improve circulation.
For some people, these lifestyle measures are enough to control diabetes without the need for medication. This isn't always the case, though; if these measures are not enough, diabetes medicine or insulin may be prescribed by your doctor. These should be taken as prescribed even if you think you feel well enough to skip them. All of these steps can help to improve how your body reacts to insulin and help to move glucose into your body's cells.