FUN is generally something you enjoy doing. Going to the cinema/shopping/parties etc etc Also a person can be FUN - you enjoy being around that person. FUNNY is generally something/someone that makes you laugh. Comedies/jokes/someone who tells jokes etc

on a very simple level: FUN (as an adjective) = enjoyable, in an entertaining sort of way. FUNNY = humerous. For example, if you like playing tennis, you might say "Tennis is fun." But tennis would not be funny, unless it is being played by clowns.