The opening scene of George Orwell's 1984 is intended to introduce the reader to three main elements of the novel.
The first element is the context, an imaginary dystopian future world. By having the narrator look out over London as it has changed under its new regime, Orwell provides the exposition necessary to explain the context of the story to readers. We learn of Big Brother, the government agencies that enforce social rules, ubiquitous surveillance, and impoverished bleak surroundings. We see the narrator's home, Victory Mansions, as depressing and dilapidated.
The second element we are introduced to is the narrator of the novel, Winston Smith, a minor bureaucrat working for the Ministry of Truth. We learn about his job and his personal life.
Finally, we are introduced to the beginning of the major conflict in the novel, that between Winston and the society in which he lives. The first stirrings of his rebellion appear as he reacts to the errant thought that he actually hates Big Brother.