Writing a screenplay - how?

I have an idea that I'd like to put to paper, but quite frankly beyond telling 9/11 conspirators how remarkably stupid they are I have no experience writing.



If I were to write a screenplay, how would I promote it, get it seen by someone who makes movies?





How would I ensure my original idea is actually original? Who would I trust? Are there any screenplays that are online where I could get an idea how it's done?



sooo many questions.