What is the difference between glycerol and glycogen?

Glycogen is a polysaccharide that is often referred to as animal starch (however this is not correct). It is the storage form of glucose in animal cells.

Glycerol is a compound consisting of a simple molecule. Used during the preparation of prescription drugs. 

(hope this helps somewhat, let me know if you need me to explain)

Three simple forms of precipitation are: Rain, Snow and Hail.

Hope this helps!