As Katlaughing knows, I'm working on a screenplay right now, my first written on laptop. I would advise doing a web-search for "Sophocles", which will give you a sample of their formatting software as well as the entire screenplay of Casablanca. I would visit the library and read as much as possible on script and screenwriting to get an idea of recommended structure, how to write the treatment (summary), organizing scenes and so forth. There is a site online that offers a formatting program called First Draft, which is meant as a free alternative to the commonly used formatting software called Final Draft. I couldn't get it to download, but maybe you'll do better. I wound up ordering software called Hollywood Screenwriter, which at $50 was 100 less than Final Draft, but is very easy to use. It doesn't offer the story creation material on the more expensive software, but I already had my story treatment done and didn't need that. I simply needed a straightforward tool to eliminate constant manual text formatting.
Good luck!