What is a Screenplay?
Most people ask me the same thing about the craft of screenwriting: What's the most common problem I find with people writing scripts? I tell them that most of the problems I encounter deal with 'telling their story in dialogue,' not pictures. A screenplay is a story told with pictures, in dialogue and description, and placed within the context of dramatic structure.
The most evident change in screenwriting within the last 10 years is this: There is no explanation needed. As a writer, you do not have to explain to the audience the thoughts, feelings or emotions of your character. No explanation. That does not mean you don't need some exposition -- that is, 'information necessary to keep the story moving forward.' A scene in the screenplay will always serve one of two functions: either it moves the story forward, or it reveals information about the character.