What happens at the start of the film?

At the start of a film, the setting is established along with the introduction of the title.

Opening credits are used to show the audience the main team such as the distributions, production team, directors, producers and cast etc. 

There usually is music and sound used to accompany the credits. 

It may also contain visuals that might give the audience an idea for the rest of the film.

For example this would be the at the start of any Walt Disney film