When you sit down to watch a film the narrative structure help defines the story. It needs to be structured to help the viewer understand the message contained within, giving the film meaning throughout. However you need to keep in mind that the narrative structure only applies to the way in which a story is told not the story itself.....meaning the narrative structure is the chronological stages or steps that progress from one to the other throughout the story.

The conventional narrative structure pointed out by Tzvetan Todorov as a rule has five stages though this can be rudimentary broken down to three stages, a beginning (state of equilibrium), middle (disruption to the equilibrium) and end (reinstate the equilibrium). What do I mean by equilibrium its simply just a state of balance, normality in which the characters find them selves at the begining.

Below is Tzvetan Todorov conventional narrative structure complete with five stages:

Stage 1
A state of equilibrium is defined.

Stage 2
Disruption to the equilibrium by some action or crisis.

Stage3
The Character(s) recognition that there has been a disruption, setting goals to resolve problem.

Stage4 The Character(s) attempt to repair the disruption, obstacles need to be overcome to restore order.

Stage5
Reinstatment to the equilibrium. Situation is resolved, a conclusion is announced.

With the five stage layout the narrative becomes more comprehensive. However its essential to remember films need to be seamless as the chain of events unfold, with all the questions raised answered and all the loose ends tied up unless you want to break the conventions, induce a cliff hangar, intentionally create doubt in the minds of the audience and leave them questioning.

Even though these stages are presented here as a linear structure there is no golden rule that it has to be this way, especially if you wish to create a non-linear structure. Should you wish to you can always muddle up the chronological order and have the end at the begining. Remember a film should have clear goals with believable chararcters if its to maintain a sense of credibility and to help keep the audience captivated.

Vladimir Propp states there are seven 'spheres of action' which characters can be well .... characterized to. These spheres are catagrised as the hero, villain, donor, helper, princess (though this can be exchanged for a prince), dispatcher and false hero. Not all spheres of action are needed to be addressed for a film as its also well to note characters can portray more than one sphere and vice versa, spheres can be composed of several characters.

Vladimir Propp seven spheres of action:

Hero: Individual(s) who's quest is to restore the equilibrium.

Villain: Individual(s) who's task is to disrupt the equilibrium.

Donor: Individual(s) who gives the hero(s) something, advice, information or an object.

Helper: Individual(s) who aids the hero(s) with their set task.

Princess (Prince): Individual(s) which need help, protecting and saving.

Dispatcher: Individual(s) who send the hero(s) on their quest.

Fasle Hero: Individual(s) who set out to undermine the hero's quest by pretending to aid them. Often unmasked at the end of the film.