West Egg and East Egg are two settlements or suburbs, named after peninsulas shaped like "a pair of enormous eggs, identical in contour and separated only by a courtesy bay" known as Long Island Sound. So, the two areas face each other across the stretch of water.
West Egg is "the less fashionable of the two." It is the location of the Gatsby mansion and the Carraway cottage. West Egg is where newcomers live - persons hoping to make their fortune, like Nick, or persons trying to convince others that they have made their fortune West Egg's residents aren't what they appear to be, as is the case with mansions like Gatsby's -
a factual imitation of some Hotel de Ville in Normandy, with a tower on one side, spanking new under a thin beard of raw ivy, and a marble swimming pool, and more than forty acres of lawn and garden.
East Egg is the location of the old money, "the white palaces" of those who truly have achieved substantial wealth. There was nothing imitation about the home of Tom and Daisy Buchanan; it was
a cheerful red-and-white Gerogian Colonial mansion, overlooking the bay. The lawn started at the beach and ran toward the front door for a quarter of a mile, jumping over sun-dials and brick walks and burning gardens-finally when it reached the house drifting up the side in bright vines
Your introduction could set the stage with a description of the land forms giving the areas their names, then go on to contrast the pretense of wealth in West Egg with the factual wealth of East Egg.