A scene signals a movement from a location or it represents a change in time. Each scene has to have a turning point, the characters must have an objective and there must be conflict within the story.
An average length for a script is 120 pages; there is approximately one minute of screen time per page. A script for a movie is made of three acts that contain a beginning, middle and an end.
Act I starts the visual introduction of the characters and the world where the action takes place. Act I introduces the first turning point, the catalyst that raises the stakes and moves the main character or protagonist forward.
Act II develops the subplot of the script. The protagonist conflict with the antagonist is developed. The story intensifies, leading to a second turning point, the dramatic revelation that ends the second act.
Act III is the dramatic climax where the protagonist must change or gain strength to overcome the final obstacle that leads to the final scene of the script.