Genre means the category on which the film is based on and sungenre is the category that is subdivided by a larger genre.
Examples of a genre: Thriller, Comedy, Romance, Sci-Fi, Action, Adventure etc.
Examples of a  subgenre: Romance; This category would have certain features that would link to comedy, drama, sexual/erotic films. A romantic film would always consist of a man and a woman who are in love and at some part have a sort of argument that would break them up, then they would get back together again and their relationship would be stronger than it was before, they would either get married or the ending of the film would show what their future is going to be like.