The opening scene establishes the setting of the film with a wide shot of the school and the voice-over saying that it is located in Illinois, USA, in 1984. Then the voice-over tells us an outline of the story, that the characters are told to write an essay about themselves during their detention, while there is a montage of shots from around the school which reveals more about the setting: we see that it is a typical American high school and that at the moment it is empty.
Before we see the characters, the voice-over describes them as "a brain, an athlete, a basket case, a princess, and a criminal". This tells us a little bit about their personalities and which stereotype they fit in to. We are properly introduced to them one by one with a short scene of them arriving at school. It is clear which clique they represent from the conversations they have - or don't have - with their family or from their actions, and it is also clear that these are the five main characters of the story.
The events in the opening scene don't follow on from each other but they are connected in a way because the same situation is shown from the viewpoint of each character.
Not too much information is given to the audience in the opening, but it is enough to interest them in the film as they have an idea of where the film is set and the situation. Most information about the characters is not revealed straight away but is developed as the film goes on.