what is the difference between insulin and glucagon

Insulin and glucagon are both hormones secreted by pancreas.

Glucagon is secreted by the alpha cells while insulin by beta cells of islets of langerhans (in pancreas).

The main difference is in their function. Insulin decreases the blood sugar level by initiating absorption of glucose by cells from blood abd its conversion to glycogen while glucagon increases blood sugar level by causing the liver to convert glycogen into glucose and release it into blood.