RSR member Chelsea was our speaker today. She talked about screenwriting. A book writer not only writes dialog, they also write descriptions, describe actions, colors, sounds, etc. However a screenwriter/playwriter mainly writes dialog. The director works with descriptions, actions, etc. The difference is that a movie or play is visual where as a book is not visual.
Chelsea talked about each genre of literature having its own set of rules (or format) and that readers/audiences are expecting that format. Thus the rules for a romance story are different from a mystery, even is the basic plot is the same.
She also gave us an introduction to a screenwriting platform that she uses (celtx.com) pointing out that there is a free version if we want to try some screenwriting.