The frame story of Big Fish serves as the realistic portion of the film and is really quite simple. Will Bloom hasn't spoken to his father, Edward Bloom, in three years because he's become fed up with his father's penchant for passing off impossible tales as his history. Now that his father is dying, however, Will visits his father, hoping that he'll finally learn the truth of his father's past.
Within this frame story, we have the story of Edward Bloom's past as told by Edward Bloom. This is where the fantasy portion of the movie appears. This story spans from Edward's birth to the day that Will is born and contains many mystical creatures and happenings.
Big Fish is, to put it simply, a really good movie. It's funny, heartwarming, and imaginative. While I laughed several time throughout the movie, but I must admit to tearing up a bit too. Despite the fact that it contains a lot of "mini stories" about Edward's past, it is well-paced, and captured my interest throughout the whole movie. It's somewhat strange at parts but in the best and most charming possible way.
And if you watch Big Fish, be prepared for a small role played by Miley (then credited as Destiny) Cyrus. It can be a bit jarring if you aren't prepared for it.