How does insulin control glucose

Insulin is normally secreted by the beta cells of the pancreas. The stimulus for insulin secretion is high blood glucose. Although there is always a low level of insulin secreted by the pancreas, the amount secreted into the blood increases as the blood glucose rises. Similarly, as blood glucose falls, the amount of insulin secreted by the pancreatic islets goes down. 

Insulin stimulates a variety of different body cells to absorb glucose from the bloodstream, thus reducing the overall glucose level. Liver cells also absorb blood glucose which it stores as glycogen.