Catch-22 is all about war: how confusing, nonsensical, repetitive, and illogical it is. Thus, the prose style in the novel matches the novel's content (we often call this "form mirroring content"). Heller's style in this novel is wordy, confusing, repetitive, and hard to follow with its jumps in time and shifts in perspective.
We see repetition in the opening lines of the novel: "It was love at first sight. The first time Yossarian saw the chaplain he fell madly in love with him." The first sentence tells us everything that we should know about the instantaneous nature of this love. Yet the second sentence tells us again, this time providing a little more information (the names of the people involved in this love). These first lines echo much of Yossarian's experience of war: the way it repeats but with slight changes and the way we learn more from each repetition.
This repetition appears in the chronology of the novel, as well. Scenes and events are related multiple times, with each new perspective providing more details and context. We often don't understand scenes the first time we read them; Heller withholds information, slowly revealing pieces of the overall puzzle as the novel unfolds. This style echoes the atmosphere of wartime: the individual events that comprise the war are hard to make sense of in the moment.
Heller also highlights the nonsensical nature of war through the flawed, circular, or contradictory logic the characters and narrator use in the book. In the early pages of the novel, Heller writes, "The Texan turned out to be good-natured, generous and likable. In three days no one could stand him." These two sentences paired together make no sense: why, if the Texan is a "likable" person, does no one like him? There are many other examples of these paradoxical sentences: "Not even Clevinger understood how Milo could do that, and Clevinger knew everything" and the exchange in which Milo insists "I never lie!" followed by "I only lie when it's necessary" are other moments.
The style of Heller's prose in this book is essential to understanding the narrative and its thematic elements, for one echoes the other. We are meant to feel confused, as if we are lacking information, and we are meant to be able to easily poke holes in the logic of the characters. In this way, Heller can heighten his satire of the war.