The novel The Brief Wondrous Life of Oscar Wao by Junot Junot Díaz begins with a prologue that contributes an overarching theme to the novel and then continues with the first chapter, which sets up the main character's early years. Let's look at some of the ways in which these two opening sections help us better understand the novel.
We'll examine the prologue first. It sets forth the story of a mysterious curse called fuku that came from Africa with the slaves in their suffering. It has affected the lives of Caribbean people ever since, and some say that the dictator Trujillo was actually the curse embodied. The narrator speaks of the horrors unleashed by this dictator upon the Dominican Republic, and he explains how the curse made its way to the United States when John F. Kennedy intervened in the assassination of Trujillo. The narrator then turns his attention to the protagonist, Oscar de Leon, and explains that Oscar's is a "fuku story." His life and his family have been affected by the curse. The rest of the novel explains this tantalizing mystery.
The first chapter presents Oscar's early life. He reaches his peak quite young, the narrator explains, during his "Golden Age" in second grade, when he actually has two girlfriends at once. Unfortunately, everything goes downhill from there. Oscar losses his confidence, gains weight, becomes shy, and ends up a quiet loner with few friends. He turns his attention to works of fantasy and science fiction and dreams of becoming a writer. The implication is that Oscar is somehow experiencing the curse, but we are left to believe that as we will.
The narrator continues the story, focusing on Oscar's depression, his relationship with his sister Lola and their mother, and his focus on his own futility. Oscar is indeed a rather pathetic character, and this chapter sets him up as such. It shows us his insecurities and desires, his strengths and weaknesses, and his tendency toward self-pity and isolation. Oscar's character is now firmly in place, preparing us to watch Oscar as he continues his journey through life. This early chapter sets us up for both predictable outcomes (like Oscar's failures in love) and some surprises later on (like Oscar's unexpected courage and willingness to sacrifice himself).