Why has Nick moved to New York?(in chapter 1)
As you say, you can find this in Chapter 1. In my edition of the book it is on page 7, in the part where he is telling about his family background. Nick says that he has come to New York (he says to the east) in order to learn the bond trade. What this means is that he will, more or less, become a stock broker (stocks and bonds are not the same thing, but both are types of investments that can be bought and sold). Nick figures that he can make it selling bonds because everyone else is doing it so why not him?