The green light is a symbol of all of Gatsby's wants and longings. It's one of the most important symbols in the book. It shows his closeness to his dreams. It's located at the end of Buchanan's dock (Daisy's dock). It's a green light that is always far away. Everyone's able to see this light even though it seems so distant from them.
The light symbolizes different things for different characters in the book. To Gatsby it represents his future, but to people like Tom it means nothing. The green light is seen over and over again during the book. "Green is the color of hope and it first appears when Gatsby stares across the bay towards a green light at the end of a dock (21, 8ff.)."
The green light is a big deal for Gatsby. He sees it as a representation of his future with Daisy and all the things he hopes for in the future. He looks at Daisy as if she's a dream that he will never reach. Although, later in the book he sees that Daisy is a posibility in his future. No matter what happens, Gatsby is forever in love with her. Gatsby often looks at this light and just thinks about his future, but forgets about the present.