Need some info on writing screenplays...

I have more than one question about screenplays, and here they are:
-I can't get a screenplay software to download because I'm stark broke, so does anyone know the basics of screenplay software?
-Who do I go to with a finished screenplay?
-How do I put a patent on a screenplay and do I need to put the patent number on the screenplay?
-What do you call a person who writes screenplays?
Thank you for your time!