A narrative structure is the term given to the way in which a film is constructed, for example the main way in which most films are constructed is with a hero or heroine being introduced to the story, this will normally be the main character that the story is based around as well as an agent of change that causes some sort of disequilibrium to the hero/heroine, this is where the problem comes into place which is later followed by the hero/heroines quest to solve the problem which then normally leads to a return to normality. This can be shown clearer in this diagram:

I will use Dawn of the Dead for example our heroine is Anna, a character that we meet at the beginning of the film as well as the survivors that she meets, the agent of change is the zombie plague that is infecting the people around her, the problem is obviously the fact that zombies are running around killing innocent people, Anna’s quest is simply to survive the zombie attack and to try to escape to a deserted island out at sea with one of the other survivors boats. The only problem with using Dawn of the Dead for an example is that there is no return to normality afterwards as in the credits we assume that all of the survivors die but we cannot be sure as the camera is dropped.

This video does a good job of showing how narrative structures work more indepth visually