Monomers are the smaller units of polymers. Repeating units of monomer helps to form a long chain of polymer. Monomer units can be identical or even non identical in the polymer but each monomer unit is analogous to the other unit. Monomers in a polymer are held together by the formation of chemical bonds (called the glycosidic bonds in case of polysaccharides) between them.
A single sugar molecule like glucose or fructose is called a monosaccharide. When many monosaccharide units are joined together, they form a polymeric structure called a polysaccharide. Therefore, a large macromolecule formed by the combination of many repeating units of monosaccharide is called a polysaccharide. For example, starch is a polysaccharide formed by the polymerization of many glucose molecules (monomer units).