In Chapter One we find out many details about Nick, the narrator for the book. We find out that he is from the West, moves East, and has recently returned. We find out that his father raised him not to judge others, because you never know what they have been through. We also discover that Nick has been to the war and to college, which is how he superficially knows the Buchanans. Based on the narration, we can assume that Nick did well in college and that he is a fairly intelligent individual, though somewhat naive about life. Because he is new in town and lives in West Egg (the less fashionable side) in an eye-sore, we can also infer that he doesn't truly fit into the society he moved to join. He dislikes the insincerity and passivity of the Buchanans and Miss Baker towards their lives and the world, and doesn't share in Daisy's pessimism.
These descriptions are important for a few reasons. One, it helps the reader determine how reliable of a narrator Nick will be. He is reserving judgment, but at the same time he is naive. It also helps us understand why he is intrigued by Gatsby, and why he eventually will return West.