The three acts are setup (of the location and characters), confrontation (with an obstacle), and resolution (culminating in a climax and a dénouement). Usually, in a two-hour film, the first and third acts both typically last around 30 minutes, with the middle act lasting roughly an hour, but today many films start from the confrontation point and then goes to the setup act or they might even start at the last act and then go back to the start.
In Writing Drama, French writer and director Yves Lavandier shows a slightly different approach. As do most theorists, he maintains that every human action, whether fictitious or real, contains three logical parts: before the action, during the action, and after the action. But since the climax is part of the action, Yves Lavandier maintains that the second act must include the climax, which makes for a much shorter third act than is found in most screenwriting theories.
Besides the three-act structure, it is also common to use a four- or five-act structure in a screenplay, though certain screenplays may include as many as twenty separate acts.