Early in the story, the protagonist, George, explains that "somebody whom he knew, although only vaguely, had been taken by a great white within a stone's throw of the edge of the beach." This is important to the story because it introduces a sense of danger to the story. George lives near the beach and likes to surf, and so after hearing about this "somebody whom he knew," the reader becomes concerned that George might also be in danger of being killed by a shark. This helps the reader to care more about, and emotionally invest more in the protagonist of the story.
Later in the story, we learn that George's girlfriend, Frizzie, also likes to surf, and we learn that there is a man who sometimes helps Frizzie to "take her (surf) board off the car if George (isn't) around." This is important because this man is the brother of the passenger who George is called to testify against. George and the parking officer, earlier in the story, see a car, occupied by a driver and this passenger, drive away from a dead body. The passenger's brother, Frizzie's friend, asks George not to testify, and tells him to "watch (his) back" if he does. This connection between George, his girlfriend, and the passenger in the car becomes vitally important later in the story, as I shall explain below.
At the end of the story, George is murdered, and the murder seems staged to look like a shark attack. This idea of making a murder look like a shark attack is an idea that George, who is a writer, himself came up with earlier in the story, for a story of his own which he started but then abandoned. At first, this seems like a tragically ironic, bizarre and inexplicable coincidence. However, if we recall that the only person George tells his story ideas to is his girlfriend ("She was the only person who he discussed his stories with before they were published") then George's strange death seems to make more sense. The implication is that George's girlfriend told her friend about George's idea of staging a murder to look like a shark attack. Earlier in the story, in fact, Frizzie asks George not to testify against her friend's brother, and George, surprised, replies, "What am I to think? That you're having an affair with him or something?" This possible affair, by the end of the story, seems very probable. The fact that George, the writer, only tells his girlfriend about his story ideas, is thus of huge importance because it is the one piece of information that allows the reader to make sense of George's death at the end of the story.