What was Holling talking about in the quote about the world sucking in its breath in The Wednesday Wars?
The quote, "There was a little pause while the world sucked in its breath ..." (p.36, "October")?
Figurative language--figures of speech--always takes some work to understand, though it is an important skill to acquire since figurative language even enters into understanding history and history's documents. One kind of figure of speech is an idiom. Holling is using an idiom when he narrates that "the world sucked in its breath." Another kind of figure of speech is a personification. Holling is also using personification when he says, "the world sucked in its breath."
A figure of speech is a phrase that has a meaning that is different from the literal words used, as you say, for example, the world cannot literally suck in breath. So the meaning of the phrase is not literal, it is figurative: it means something other than the definitions of the words suggest. [Metaphors are another figure of speech.] Idioms are phrases that are culture-based and have figurative meanings. The fact that Holling personifies the world makes it a little harder to sort the idiom out, so first let's look at personification.
Personification figuratively gives human attributes to non-human objects. In this case, Holling gives a human physiological quality to the world: the world breathes like a human breathes, which, as you've said, is not literally possible. So the figurative idiom applied to the figuratively personified world means that the world suddenly drew in its breath with a vacuum-like energy during the "little pause." The import is that you can form a mental image of the world as a character reacting with Holling to events as they occur.