I am assuming you are asking about the written structure of the play. Shakespeare's tragedies followed the pyramid formula with the exposition occurring in Act I followed by the rising action in Act II. In Act III the climax occurs which leads to the falling action in Act IV and the final resolution, or denoument, in the final Act V.
Exposition sets up the background of the story, introduces the characters and the chief conflicts. The rising action presents events that spring from the chief conflict but that often produce grave consequences. The chief 'point of no return' occurs in Act III when the character creates for himself a situation which he cannot undo. The falling action reveals the swiftly compounding consequences resulting in a resolution in Act V. In a tragedy, this resolution is often death and the restoraton of order by some outside party.