The mood is the way the story is set up. It gets you in the right mood for the story.
An Example of mood would be "It was a dark and stormy night." This sets up the mood of the piece as gloomy, dark, and probably scary.
Another example: "The air was clear and crisp, and patches of sun filtered through the trees." The mood here is probably more calm, light, and happy.
Mood doesn't always have to be imagery, but those are the example I could come up with off the top of my head.
I hope that this helps!
