The use of music of in films:
Music in films are very important to not only tell a story but they can also influence characters moods and development also, it can enhance the scene.
Back when films were silent, music was used heavily to move the film along, it helped tell the story plus when something happened to a character, the music would change to fit the mood.
Music is usually made for the film in question but, sometimes songs made by singers can be used if it fits the tone of the film. The lyrics of a singer could imitate how the character is feeling or what's going on in the film.
Characters sometimes can break out into a song if the dialogue alone can't explain how they are feeling or if they want to express themselves better.
Music can also help people remember certain films, long after seeing them. Examples would be the theme song to Star Wars or the soundtrack to the first Grease film. Audiences old and new always seems to remember the soundtrack to the films well and it helps pass the films on from generation to generation.
The environment is also important to the music score, depending on where the film is set, it must have the appropriate soundtrack to it. So, a horror film will have slow, eerie music while an action film tends to have faster paced music and Sci-Fi has futuristic music to make it sound like the movie takes place in the future. All these things help to make a movie more believable and it helps fit the tone and mood of a movie.