'What is an opening sequence?'

The opening sequence of a film is usually the most vital part of a film and it is in place in order to hook the watcher and keep them viewing the film. 

An opening sequence can establish the place and time of a film and set the scene for the whole film ahead either with the images that are shown are using a range of narrtive devices, including captions, dialogue and voice overs. This scene can also create enigmas and other questions that the viewer wants to know the answer to. 

The section of the movie is also frequently used to introduce characters, these may be the main character or a character that reappears later in the movie again creating more enigmas and mystery around these characters. The chosen genre is enforced strongly in this scene with use of cinematic style, costumes and location.

(Taz)