When is the setting of The Hunger Games introduced? Why is it important?
Setting will generally encompass two areas. Where does the story take place and when does it take place? For The Hunger Games, the when is not very specific. The reader knows that it takes place some time in the future, likely one hundred or more years after present day. The reader knows that the United States existed and broke apart to become Panem and the 12 districts. That immediately puts the book in the future, but how far into the future is not explicitly stated. That's probably a good thing, because when an author puts a date on future events, and that date finally rolls around looking nothing like the book, I think it feels a bit weird (case in point, George Orwell's 1984). By having The Hunger Games take place at an indeterminate date, a reader in any decade may have in their mind "this book's society's degeneration could still happen to the U.S." The other thing that placing this book in the future does is put the book smack in the middle of an entire genre: post-apocalyptic literature. That's the genre where the future has basically imploded on itself, and society has actually moved backwards. It's a depressing genre, because it paints a picture of society getting worse. Who wants that?
The Hunger Games takes place in the former United States. It is now called Panem and has been divided into 12 districts, each with their own role in manufacturing. The goal is to support the Capitol. That nutshell view of the story's location is important because it is a structure that sounds familiar to readers. First, states and a Capitol are what the United States is. Second, it's also reminiscent of ancient Rome. Rome was the Capitol in charge of a large empire of states/areas/provinces/etc. To help rule that much area, Rome worked to keep the population fed and happy. That would keep the people docile. Panem doesn't quite keep everybody fed and happy, but is making the attempt with the annual Hunger Games.
Most of these setting details are outlined right away in Chapter 1, but little details about the Capitol and its rule are sprinkled throughout the first third of the book.