What are the differences between glucose, glucagon & glycogen? explain simply

Glucose is the type of sugar our bodies use for energy. glycogen is the form that our livers store glucose in, to use later. 
glucagon is a hormone made in the pancreas that tell the liver to break down and release glycogen. in most people, the pancreas make more glucagon when blood sugar is low, but it makes some glucagon all the time.

hope this helps. 

Glucose = releases sugar
Glucagon = tells liver to release glycogen
Glycogen = a hormone release by pancreas which does the same job as glucagon