Writing a screenplay isn’t like writing prose but what is it ? A screenplay is a written ‘visual record’ of what will be seen on camera as a film, cable or TV show.
Start with a treatment, an outline of perhaps 10 pages, much shorter than 100 pages of screenplay will give you a chance to stress test your work.
1. Concept: state in one sentence what your story is about
3. Plot : acts, opener and story
https://nofilmschool.com/film-treatment is a good place to start
Screenwriting software chooses fonts, margins, indents, and spacing depending on what you are describing, scene, shot or transition.
Competitions are regularly updated and cover all genres. Scriptlab is also a source for information on all things scriptwriting including examples.