Bucks life is already rolling along before the story begins. Bucks status quoe, life as usual is his initial situation. This situation may be a foreshadowing of things to come or may be a contrast to the things to come. The initial situation may motivate Buck to make the choices that drive the story. For example if he is a prisoner he may be motivated to escape.
In The Lord of the rings the story starts in the Shire. The peaceful shire is a strong contrast to the dangerous and chaotic places encountered later by Frodo.
Here are some classifications of general situations.