Nick is the narrator in The Great Gatsby, so we see Gatsby's world through Nick's eyes. This is the primary method Fitzgerald uses to give the reader information about Nick and possibly about Fitzgerald's own personality. Nick is intelligent but an idealist. He prides himself on being honest and trustworthy. He realizes, throughout the course of the novel that one must reserve judgments about others to give them a fair chance but also because there is often more to a person's life story than is initially evident. This is most dramatically realized when Nick learns of Gatsby's past.
In consequence, I'm inclined to reserve all judgments, a habit that has opened many curious natures to me and also made me the victim of not a few veteran bores. (Chapter One)
Nick is therefore a relatively reliable narrator. In Chapter 3, Nick goes to one of Gatsby's parties. He remarks that he, unlike most of the people there, was actually invited to the party. Nick marveled that these people, some of whom had not even met Gatsby, could come to his house as if it were an amusement park. Nick felt self-conscious and awkward which shows that he considered his host's (Gatsby's) feelings and felt that most of the party-goers were just using Gatsby's home for their own amusement.
Nick finds Jordan Baker at the party. They talk with others who all speculate different stories about who Gatsby really is. The fact that their stories don't match up shows that they know nothing about their host and it increases the mystery surrounding Gatsby. This sparks everyone's, including Nick's, curiosity.
We also learn that Nick spends most of the summer alone. He would take walks on Fifth Avenue and fantasize about women he saw. He spent some time with Jordan Baker. Although realizing how dishonest she was, he found something alluring about her. This chapter confirms that Nick is thoughtful and really does try to avoid judging people, as he does with Jordan. Nick is thoughtful, not judgmental, and in describing his experiences in this chapter, he concludes, "I am one of the few honest people that I have ever known."