Characterization is the method used by a writer to develop a character. Screen writers use both direct and indirect characterization in their screen plays. Direct characterization is when a narrator or actor "tells" you exactly what it is that they are thinking. Indirect characterization is when the audience learns about a character through the following:

(1) showing the character's appearance,
(2) displaying the character's actions,
(3) revealing the character's thoughts,
(4) letting the character speak, and
(5) getting the reactions of others.

The distinction between direct vs. indirect characterization can be thought of as the difference between "showing" us a character and "telling" us about that character. Remember that film is a visual medium, so in general, showing will always be the most powerful of the two.

Please read the following article: Character Driven Screen Plays when thinking about how to develop the character arc and visual arc of your story.