For the planning of plots of Fitzgerald in his The Great Gatsby, it appears to me that he intends to introduce his main characters to us in the first two chapters:

Chapter 1:
Upon the reading of the first few pages of Chapter 1 I am wondering who this narrator is, is he the protagonist, is he Gatsby himself? Is this story happening in England or America? With no more pages to go I’ve come to answers to those questions and more.

The narrator’s name is Nick Carraway, he is employed by the author to develop and explore the story. Daisy and Tom appeared to be a happy couple(to my impression), as they are wealthy, young, but it turned out not. They are only rich but are not living a happy life. Reason is that Tom has got his own woman in New York. Tom’s un-loyalty to his wife seems serving as a moral excuse for Daisy's affair with another man (which is revealed in later chapters).

Jordan Baker is a supporting character. The main character, the protagonist, Gatsby, is not showing up, but exists everywhere.

Those people live either in West or East Egg near New York where mostly rich people can afford to live, especially in East Egg.

It looks like that the author pulls open the curtain on the stage and several characters of Nick, Daisy and Tom and Jordan, etc. are presented, plus where and when the story happen. An unquiet evening indicates the starting of an undetermined story, turbulent or other, read on.

Chapter 2:
The introduction of Tom Buchanan’s mistress, Myrtle.