The Crucible, by Arthur Miller, is a play written in four acts. Each act serves to move the plot forward, and the events which begin and end each act correspond to the key elements of any literature plot diagram.
Act One of the play begins with the exposition, the introduction of all the major characters, and ends with the inciting action. The girls, to avoid getting in trouble, begin the accusations that will soon overtake the entire town.
Act Two starts eight days later, and we learn that the town is reverberating with accusations of witchcraft. This act is full of rising action, culminating in the arrest of Elizabeth Proctor and John Proctor's insistence that Mary Warren will tell the truth. Now the story has begun to affect the main characters of the story, and most would say this is the turning point/crisis/climax of the story.
Act Three is set in the courtroom, and it displays the consequences of Proctor's affair with Abigail. When Elizabeth lies to save her husband's life, the chapter ends, the falling action is finished, and Proctor's fate is essentially sealed.
Though it is a dramatic ending, Act Four is simply the denouement, the tying up of loose ends. Here we see Danforth continuing in his pride, Parris acting almost as selfishly as always, Abigail running for her life, Hale pleading to save innocent lives, Elizabeth and John loving one another again, and the innocent victims of this awful episode dying with their souls and names intact. John Proctor can once again "see some shred of goodness" in himself, and that is the final resolution of this story.