Cellulose and glycogen are both polymers (polysaccharides) which are made of smaller molecules called monomers (glucose), although they differ in their functions and scructure.
Cellulose is found only in plant cells, while glycogen is detected in animal and fungi cells (or plant cells without chlorophyll). While cellulose plays structural role (makes up about 30% of the plant cell wall), glycogen has energetic function being a storage of energy of fungi and animals.
The molecular formula of cellulose is (C6H10O5)n.
The molecular formula of glycogen is C24H42O21.
Cellulose consists of thousands molecules of beta glucose, glycogen is a chain of alpha glucose monomers. Cellulose monomers (beta glucose) are connected with 1,4 glycosidic bonds, while glycogen has 1,4 and 1,6 glycosidic bonds between its monomers. Cellulose is a linear molecule, its chain is unbranched. Glycogen is made up of many branched chain, these branches can form coils. Cellulose molecule is much longer than glycogen. Highly branched chain of glycogen allows this polymer to dissolve in water while cellulose is insoluble.