Todorov's Narrative is not just a basic Media Studies theory - you'll have encountered versions of it throughout your English education, even at primary. It's a good theory to know at GCSE, while at A-Level, you should refer to it by name if relevant.
Almost 2,500 years ago, Aristotle said that stories have a beginning, middle and end - and all this time later, it's still a framework taught in most schools. A story begins somewhere with a character, some unusual things happen in the middle and then we are left to see how the character or their world has changed by the end. Todorov's Narrative Theory is simply a slightly more detailed version that recognises the spaces in between the beginning and middle and then the middle and end. As such, his narrative theory is five steps instead of three. He suggests that stories are only stories because they are unusual events for the characters and place that they affect. Consider that everyone's daily routine of wake up, get ready, go to school/work, go home, go to bed is not an engaging narrative because it is very normal. If something unusual were to feature in this otherwise routine day, then we have an interesting story.
Todorov calls this normality equilibrium. All stories start with this equilibrium. It's a normal day. Nothing our of the ordinary is happening. In simpler terms, it's the beginning of the story. Todorov then adds a step and says that something disrupts the equilibrium. Things stop being everyday, normal and ordinary. In terms of the middle of the story, Todorov expands on this by saying that the characters recognise the disruption. They become aware of the fact that it's no longer a normal situation and respond to this emotionally. Todorov adds one more step, saying that the characters try to repair the equilibrium. We all like things to go 'back to normal' and dislike change, and will do whatever we can to put things back to how they were. The story then finds its ending. Todorov expands on this by saying that the ending is a new equilibrium. This is important, as one of two things can happen when the characters try to repair the equilibrium: either they succeed, and things go back to the way they were. More often than not, however, their success (or failure) changes things, and a 'new normal' results. Of course, that new equilibrium could be disrupted again - but that's a story for another time! Let's see that in action with a really simple narrative that also brings in some elements of Propp's character theory! My notes are in italics and aren't part of the story!
It's a normal day in the kingdom. The prince is having a very ordinary day in his castle. This is his equilibrium - and it's about to be disrupted. A messenger brings news that the beautiful princess in the next kingdom has been kidnapped by an evil witch who commands a fire-breathing dragon. The equilibrium has just been disrupted! It is no longer a normal day for the prince. The prince sets out on horseback to the witch's fortress in order to rescue the princess. The prince has now recognised the disruption. On arrival at the castle, the knight battles the dragon and defeats it, freeing the princess. The prince is attempting to repair the equilibrium. The prince rides away with the princess, but asks for her hand in marriage. She instead returns home with him. A new equilibrium has been set. The days become normal for the prince once more, with the added difference that the princess is now in his life.
In summary: Todorov's narrative has 5 steps and is an evolution of very old narrative theories. Todorov says that stories begin in equilibrium. This equilibrium is disrupted. The characters recognise this disruption and then try to repair it. They either restore the old equilibrium or - more likely - create a new equilibrium.