The opening paragraphs of the story depict Tom Benecke and his wife Clare in their small apartment in New York City; he is struggling to focus on some work for his job, and she is preparing herself for an evening out.
Tom is typing on his typewriter a little bit, feeling hot, looking out his window to the street eleven stories below, and realizing that he feels guilty for working instead of going along with his wife to the movies. Clare is putting on a slip and some pretty earrings, and she's smiling and talking to Tom--she doesn't mind going out alone, but she wants him to have fun and see the movie, too. We understand that their relationship is loving and playful: he notices her beauty as she stands in the hallway; he drinks in the scent of her perfume as he hugs and kisses her goodbye for the evening; he gives her "a little swat" as she leaves. Their relationship is clearly a good one, but the fact that they're not spending the evening together is an oddity worth noticing.
A few instances of foreshadowing occur as the story begins. First, Tom has trouble opening the window when he wants to get some fresh air. We'll see later that this window's finicky, old stubbornness becomes a major problem once Tom wants to get back in through it. And second, Clare tells Tom that he works too much and too hard. Through his harrowing experiences outside the window on this evening, Tom will realize just how true Clare's words are; he'll come to understand, as he endangers his life, that he does spend too much time working and that he ought to be spending his free time with Clare instead.
You can think of the story's exposition as complete by this point; the rising action begins with the inciting incident of Tom's yellow sheet of notes getting blown out of the window.