Well, hopefully you would know the outline of the plot from reading the book, but I will give you a short synopsis to help you research further.
The Great Gatsby is a story of the pursuit of the American Dream (happiness) through the pursuit of love, money, and pleasure. The story is told through the eyes of Nick (a moral Midwesterner) but it is about Jay Gatsby who represents the striving American in all of us.
The exposition (or background information the reader needs to know to understand the story) is somewhat told in flashback through Jordan. Jordan tells us of a young soldier Gatsby who falls in love with the Southern Belle, Daisy. He is poor, and she is rich (which is a problem). Gatsby is sent to war, and Daisy gets tired of waiting so she eventually marries someone in her "old money" world and Gatsby comes home crushed that he has lost her.
The inciting moment (in my opinion) is when Daisy and Gatsby meet again in Nick's house after Gatsby has become wealthy and they start their affair.
The Climax (in my opinion) is the confrontation between Tom and Gatsby in the hotel, when Gatsby admits that he and Daisy are involved. Daisy can't choose between them and dashes off in the car while Gatsby follows. Daisy eventually hits Mrytle with the car.
The turning point is when Gatsby is shot by Mrytle's husband and we know now that the dream has come to an end.
The denouement (or falling action) is the funeral and Nick's decision to move back to the Midwest. We see in his narrative how sad it was that no one attended Gatsby's funeral...even though a few months before they all partied at his mansion. It is a melancholy look at the hollowness of the quest for wealth.