A resin is a mixture of multiple chemicals and a polymer is a polyester derivitive. Also, Resins are products that are produced by a condensation reaction. Resins are synthetically produced products.
Resins are often derived from plants. Polymer is an all-encompassing term for a type of large repeating molecule. Technically resins are polymers, but usually the word polymer is used to refer to plastics that are composed of molecules that are usually larger than resins.