Class and social standing are important themes in this novel and present conflicts to almost every main character. East and West Egg symbolize two different levels of class and social standing. Tom and Daisy live on East Egg where the people are well-bred and have class and family money. Nick and Gatsby live on West Egg where the people are "nouveau riche" - that means, they have money but not breeding. The green light shining from East Egg represents the envy Gatsby feels towards what he has always wanted -- the woman that he never gets. The water symbolizes the barrier between East and West Egg that keeps the characters apart from one another and from their desires.
"I lived at West Egg, the—well, the less fashionable of the two, though this is a most superficial tag to express the bizarre and not a little sinister contrast between them."
In describing his house, Nick says:
"My own house was an eyesore, but it was a small eyesore, and it had been overlooked, so I had a view of the water, a partial view of my neighbor’s lawn, and the consoling proximity of millionaires—all for eighty dollars a month."
By contrast, he describes Daisy's home thusly:
"Across the courtesy bay the white palaces of fashionable East Egg glittered along the water, and the history of the summer really begins on the evening I drove over there to have dinner with the Tom Buchanans."
Nick says that when he came back from his trip back east, he was changed. Where he once thought himself tolerant, he now found that he wanted things to be more even in the world. He says:
"When I came back from the East last autumn I felt that I wanted the world to be in uniform and at a sort of moral attention forever; I wanted no more riotous excursions with privileged glimpses into the human heart."
At the end of the novel Nick is no longer tolerant of everyone, especially people like Tom and Daisy. They have destroyed his faith in humanity and turned him into a rather jaded individual. He says:
"They were careless people, Tom and Daisy—they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made. . . ."
Read the novel at the beginning and at the end to see the changes in Nick. This should get you started.