3 Act Structure research

The three-act structure is a popular screenwriting technique that revolves around constantly creating set-ups, conflicts and resolutions. With this structure, a novel/film is divided into three acts: a beginning, a middle and an end.

Act 1: Beginning

We create a problem for a character and/or the audience.
Who's the main character? What's his problem? How does it become his mission in the story

• First ¼ of story
• Who are the major players?
• What is (are) the major problem(s)
• What is the narrative enigma— Will the boy get the girl? Will planet earth be destroyed?
• Major themes introduced
• A mood is established
• Conventions are established such as voice over, moving camera

Act 2: Middle part of the story       

• At least ½ the entire story
• Struggle to achieve the solution to the problem
• Further complications to finding the solution
• The cycle of struggles and complications are called reversals

Act 3: The End

• No more than ¼ of the story, usually less
• The conflict or problem is resolved
• Final crisis (or "rising action") plays out to climax; then to resolution
• Narrative closure
• Narrative aperture

I found this video clip on YouTube and it is very good in explaining the Three Act Structure. It is quick and gives clear examples of the each acts and how they can be explained in a story.