What is a Title Sequence? (3)

A title sequence is everything that appears before the film actually starts. It's like a story before the actual story.
Making it key aspects of a film, as it influences the atmosphere/feel you get from the film prior to actually watching it.
 They tend to show the audience, characters that are going to be in the film, as well as the location, on historical period(time) of the film set.
Generally gives you information on the crew involved in the production.
In regards to characters. It give us insight to the main ones. Or significances their importance. Which in a sense kind of promotes a actor/actress in hopefully making a leading debut in the future. Meanwhile offering, a taste of what to expect later in that film.