3. Purpose of film openings and title sequences

The main purpose of a title sequence is to set an expectation for the audience, and to make you forget about everything else when watching it. 
It is supposed to set the idea, but not give too much away, as it is usually at the beginning of a film.
It engages the audience if it is edited in a way that makes them feel as what they are seeing is real, even though it isnt. 

A film opening creates a scene and location in a way, again, not giving too much away. You can hear noises, that might determine the genre, characters are usually introduced. also, an atmosphere and tone is set.

The main things we expect to see is a production company name, production team, film title, and maybe the names of the cast (main character(s)), and images related to the film (if any).