Differences between movie openings and movie trailers

The difference between movie openings and movie trailers are that the trailers give a basic overview of the story showcasing some of the main characters and some of the most important scenes from the film with a brief showing of the beginning. It is used to build tension and shows progression in time along with important parts that contribute to the movies story heavily. Movie trailers also include a lot of dialogue and music to build hype and anticipation for the films release.

An example of a movie trailer with these factors included is the trailer for:

Spider man: Homecoming:

In this trailer you can clearly see the main characters have been shown with a mixture of different scenes from the movie that showcase some important parts that may be significant to the movies story line along with up beat music to excite the audience. It also shows the release date of the movie which is always included in trailers along with the main companies that made the film and of course, reveals the title of the movie mostly at the end of the trailer. Sometimes there will be a small explanation of what the movie is about, for example, in the Kong; Skull Island trailer, every few seconds a word will appear which spells out the sentence 'We Dont Belong Here' which indicates whats in store for the movie. 

Movie openings are different because they barely have any dialogue and music, generally they would set the scene and list the main/important members of the production such as the director and some of the actors along with the companies that help produce the movie. Not much is said about the plot or nothing much is shown either so that it has room for the rest of the movie to be shown.
An example of a movie opening would be the opening for Spider-man (2002):

In this opening you can see the obvious factors of a movie opening such as the most important people and companies related to the film such as Marvel, Colombia and then the title. It then showcases some of the actors in order of importance so for example, Tobey Maguire who plays Spider-man will be shown first because he is the main character. After that we can see images of webbing and vague images of Spider-man being shown which showcases the main character and his environment but does not give away any important details before the film is even shown.