If you read the first chapter, Nick himself tells us why he decided to move East and what in particular his goal or intention was. Having returned to the United States after participating in the Second World War, he finds that he returned "restless" with a widened perspective of life that had changed him and the way that he regarded the world. Note what Nick tells us about how his feelings about his home in the Middle West had changed:
Instead of being the warm center of the world, the Middle West now seemed like the ragged edge of the universe--so I decided to go East and learn the bond business. Everybody I knew was in the bond business, so I supposed it could support one more single man.
What is interesting is the way that Nick's war-time experience opened up the world to him, and led him to seek life in the thriving East of the America, but at the same time his choice of career and his intention seems curiously vague and unspecified. Note the use of the verb "supposed": it is clear that Nick is joining the bond business not because he feels passionate about it but simply because he needs something to do and he might as well do what everybody else was doing. This vague listlessness is interesting to remember as we continue to build up a picture of Nick in the novel.