"How to Write a Screenplay"

At the link below shows the basics of writing a screenplay. It helps explain the basics behind Action, Characters, Plot, Dialouge, and everything else that makes a good screenplay. There is also a good introduction to what makes a good screenplay and how to make a story flow.

"There is always something at stake in a good movie. Not just something someone wants, something that must be acquired, no matter what the risk, as in Indiana Jones and the Raiders of the Lost Ark. Or something highly desired by as many main characters as possible, like the small black statue in The Maltese Falcon. Some times it can be an intangible thing, like the freedom of a people in Lawrence of Arabia or Gandhi. All these things drive the character's quest, even gives the hero superhuman strength. It can be something personal (romance) or for the good of all (saving the world from aliens) but it must be powerful and grow more desperate as the story unfolds."

More info in the link below
http://www.screenwriting.info/