Elementor as a page builder will allow you to edit any normal page or post ( but not archives or products ) in the Prime site.
So you can create a new page and add content whilst keeping the GP header / navigation and footer for example. You’re just building content within that.
Elementor as a Theme Builder will allow you to create templates to replace things such as the Single Product page, again you can keep the theme elements for header, footer etc or you can recreate them within Elementors theme templates.
Personally i would look at creating a landing page with Elementor first before looking at replacing theme templates as that can lead to complications.