There's a law in physics called Newton's Third Law of Motion, which states that "for every action, there is an equal and opposite reaction.' Which means, basically, that everything is related. We exist in relationship to each other, we exist in relationship to the Earth, we exist in relationship to all living things, and we exist in relationship to the universe.
A screenplay is a whole, and exists in direct relationship to its parts.
How to set up a story?
The first ten pages set up the entire screenplay.Act I is a unit of dramatic action that is approximately twenty or thirty pages long; it begins at the beginning of the screenplay and goes to the Plot Point at the end of Act I. It is held together with the dramatic context known as the setup.
This unit of dramatic action sets up a story; it sets up the situation and the relationships between the characters, and establishes the necessary information so the reader knows what's happening and the story can unfold clearly. The first ten pages of screenplay, as mentioned, establish three specific things. The main character is introduced so we know who the story is about.