May I ask what you find difficult about the navigation in the site? My thinking process is that I have questions, so I want “Help” along the top right. Near the top of the page I see a heading for “Common Questions”, some of which pertain to purchasing. In reading that list, I come across one in particular, “Will my licence work with both Mac and Windows versions?” that seems like it might address what I want to know.
In the course of reading that, I see a link featured to an article on “Crossgrading Scrivener”. That goes over eligibility, which you might not qualify for if you are indeed talking of having never used a Mac, and only having the mobile version presently.
As you will note on the Products page for Scrivener referred to above, when clicking “Download Free Trial”, the only operating systems listed are Mac, Windows and iOS.