After feeling excited about the prospect of going to the Araby bazaar, the unnamed young narrator ends up feeling thoroughly disillusioned and disappointed by the time he finally reaches his destination at the end of the story.

After Mangan's sister, whom the narrator fancies, motivates him to go to the bazaar, the boy's imagination is filled with thoughts of the Araby bazaar and all its associated excitement and exoticism. For an all too brief period, the young lad is promised a tantalizing glimpse into a different world, a world far removed from the shabby lower-middle-class Dublin life that he normally leads.

But once he finally reaches the bazaar, his hopes and dreams suddenly evaporate. Due largely to his uncle's late arrival at home that evening, the boy misses the bazaar, which is in the process of closing down by the time he gets there.

One of the merchants asks him if he would like to buy anything, but the boy's heart is no longer in it. The large, darkened hall has been stripped of romance, and so it would be inappropriate—and perhaps impossible—for the boy to fulfill his original quest and buy something special for Mangan's sister.

Feeling thoroughly disillusioned and humiliated by the experience, the boy can only gaze into the darkness, his eyes burning with “anguish and anger.”

In "Araby," how is the conflict of the story resolved when the boy goes to the bazaar?

With the hopes of bringing Mangan's sister a gift from the bazaar, the narrator recalls, 

[T]he syllables of the word Araby were called to me through the silence in which my soul luxuriated and cast an Eastern enchantment over me.

However, when he finally arrives after being delayed by the late return home of his uncle on Saturday, significantly, he must spend more for the price of admission than he has hoped.  Then, to his dismay, he discovers that most of the stalls have already closed and "the greater part of the hall was in darkness."  Instead of an exotic setting, the narrator finds men counting money under a curtain for a booth with a French title used to connote the romance and risque temptations of Paris; in addition, shop girls sit idly and engage in trivial gossip.  It is at this point that the youth realizes that his "stay was useless."  Looking "humbly," he turns and departs in the darkness of the hall as two pennies "fall against the sixpence in [his] pocket."

In these crushing moments of disillusionment in the supposed exotic bazaar, the narrator reaches an epiphany: 

I saw myself as a creature driven and derided by vanity....

With a sudden realization, the youth recognizes his romantic ideas in which he has dressed the mundane with images of sacredness.  Mangan's sister is not saintly; she wears silver bracelets, symbolic of money and the mundane, and she is not the "grail" for which he seeks. Instead, like her name, suggestive of the Irish romantic poet James Clarence Mangan who wrote of doomed love and despair, thoughts of her now affect the narrator's disillusionment. And, unlike "Araby," the bazaar is a cheap imitation where mere trinkets are sold.

What happens at the end of "Araby" when the boy is at the bazaar?

Towards the beginning of the story, the young narrator has a brief conversation with Mangan's sister, who tells him that she cannot make it to the Araby bazaar. The narrator is infatuated with Mangan's sister and promises to bring her something home from the bazaar. Following their conversation, the naive, idealistic narrator allows his imagination to run wild as he fantasizes about winning Mangan's sister's heart and impressing her with something unique and rare from Araby. The narrator becomes anxious about the bazaar and struggles to control his emotions while he waits for his uncle to return home. Finally, the narrator's uncle returns home and gives him money to attend Araby, which is closing once he arrives.

The narrator likens his journey to a religious quest but is crestfallen when he arrives at the empty, desolate bazaar. The narrator then approaches a stall and overhears an English shop-girl engaging in small talk with two boys. The young woman then asks the narrator if he would like to purchase anything and he responds by saying "No, thank you." After overhearing the young woman's casual banter with the two men, the narrator experiences an epiphany and recognizes that his brief conversation with Mangan's sister was meaningless like the shop-girl's shallow discussion. The young narrator loses his childhood innocence after acknowledging that his fantasies were simply illusions and accepting the futility of romantic ideals. His exaggerated expectations concerning his devotion to Mangan's sister are significantly deflated and he experiences an overwhelming sense of alienation and loneliness as he leaves the bazaar empty-handed.

What happens at the end of "Araby" when the boy is at the bazaar?

For the narrator, there almost seems to be something magical about Mangan's sister. He describes her "figure [as] defined by the light from the half-open door," while her "dress swung as she moved her body, and the soft rope of her hair tossed from side to side." It almost feels like time slows down for him as he watches her move because he describes it in such detail. She is often defined by light. He has never spoken to her, "and yet her name was like a summons to all [his] foolish blood." The narrator even seems to think of himself as a kind of hero, imagining that he "bore his chalice safely through a throng of foes" when he is really only carrying his aunt's purchases, and Mangan's sister's name "sprang to [his] lips at moments in strange prayers and praises which [he] did not understand." He would cry, for no reason that he could tell, when he thought of her, and he felt "confused adoration." In short, the narrator thinks of her as special, thinks of his feelings for her as special, and thinks of their story as special. When they finally speak and she mentions the Araby bazaar, he thinks of it as special too.

However, when he arrives there—late because his uncle was late to come home, later still because the train was delayed and then moved slowly—he realizes that it is not special, that it sells the same "porcelain vases and flowered tea-sets" that one could purchase just about anywhere else. He listens to the cheaply flirtatious conversation of the young woman and men at the stall and hears a "voice call from one end of the gallery that the light was out. The upper part of the hall was now completely dark." The symbolic light that had once lit up Mangan's sister is gone now, replaced by the darkness. The narrator realizes that his feelings were not special, and that the world will not stop or even care about his feelings (symbolized by his uncle's forgetfulness of how important the bazaar was to him, of the late train). He had seemed to believe that he was special and that he would be able to find something brilliant and unique for his special girl, but he realizes that this was mere vanity.

What happens at the end of "Araby" when the boy is at the bazaar?

I can understand your confusion--this story does have an ambiguous ending.

There is a summary of this story at: http://www.enotes.com/araby/summary. This may help you.

What happens at the end of "Araby" is what James called an "epiphany"--a flash of internal revelation or understanding. After the young boy has revered and almost worshiped Mangan's sister, he overhears a flirtatious and shallow conversation at the bazaar between a young woman and two young men. The narrator tells us that he does not purchase anything for Mangan's sister and that "Gazing up into the darkness I saw myself as a creature driven and derided by vanity; and my eyes burned with anguish and anger."

This moment at the fair has made the boy view his feelings differently--he sees his conversation with Mangan's sister as equally silly and shallow, and realizes that she probably did not take him seriously. It is a "growing-up moment" for this young boy.