A tragedy is all about sad, sorrowful events whereas a comedy is all about happiness. Comedy aims to amuse the readers or audience. But tragedies, in most cases, teach some important lessons of life, by arousing a sense of pity and terror.
Tragedies are more serious and thoughtfully constructed than comedies and comedies are generally closer representations of everyday life.
In typical comedy plays, the characters will reunite in the end, i.e., a happy ending.But in a typical Greek or Shakespearean tragedy the fall of the protagonist is very likely in the end.