Nick and Daisy are distantly related to one another. We learn this in the first chapter, when Nick says,
Daisy was my second cousin once removed (10).
Nick goes on to explain that he had known Tom, Daisy's husband in college and that after he had returned from World War I, he had spend a few days with them in their Chicago home. When Nick decides to go East, it is natural that he would look up his relative and his old college friend.
This chapter really sets the stage for one of the themes of the book. All of these people are related or connected in some way, and all of them are of the same approximate class. The reader can see that these characters and many others of their "set" are not necessarily nice, smart, or hard-working, but that they all accept one another easily. Gatsby stands out quite clearly as an outsider.
Nick and Daisy are second cousins once removed, and Daisy's husband Tom is a college friend of Nick's from when they attended Yale together. Nick says he spent two days with them after the war in Chicago. He calls them "two old friends whom I scarcely knew at all."
In this chapter, Daisy and Tom offer some insights into Nick's past in Chicago that point to his possible unreliability as a narrator. Tom and Daisy both insist that they had heard rumors in Chicago that Nick was engaged to be married. "We heard it from three people," Daisy says. Nick denies it but also mentions to the reader that this was one of the reasons for his move East. He seems, despite all his assertions of honesty, to have at the very least been leading the young woman in question along.
At the same time, he is "touched" that Daisy and Tom know this rumor; it makes them seem less remotely rich to him.
What is established is that Tom, Daisy, and Nick (as well as Jordan) are all from the same "set," which will be important in this novel when it mentions class distinctions later.
In F. Scott Fitzgerald's classic The Great Gatsby, Nick Carraway, the novel's narrator, describes his first visit, upon moving from the Midwest to Long Island, New York, to the palatial estate of Tom and Daisy Buchanan. As Nick notes in the first chapter of Fitzgerald's novel, "Daisy was my second cousin once removed and I’d known Tom in college. And just after the war I spent two days with them in Chicago." Daisy, of course, will come to play a major role in Nick's tale of life among the elite of New York society and of the fascinating figure of Jay Gatsby. Gatsby's obsession with the unattainable Daisy, and Nick's gradual discovery of his new neighbor's past -- a past that involved considerable wealth accumulated through criminal activities and an identity vastly different from that presented to the public he sought to deceive -- provide the content of Fitzgerald's novel. Daisy, a vacuous but beautiful and vivacious woman, will ultimately prove the instrument of Gatsby's doom.