This is like a fight with no rules! Sort of...
Screenwriting sits in one of those places where there are general agreements and guidelines, although no one is keeping tabs or owning the rule book. There are just too many sides, which makes a treaty almost impossible.
Further to that, with the progression of technology on and off set, how a screenplay is presented changes with time. Add to that the ever busier script reader being asked to feed the machine for financial success, and we have an ever changing playing field. Thus screenwriting format is a bit of a moving target, but there are formatting basics and some loosely agreed rules.
But there's got to be a starting point, right? I strongly believe that if you maintain clarity, efficiency, and consistency you will be off to a great start.
Once you learn the basic aspects of maintaining clear writing, with efficient descriptions, all under a consistent presentation and approach, you have the foundations for great screenwriting!