Think of these as ways to lower duplication, so you can reuse parts of pages across muiltiple pages. Layout pages are like the outer shell, content pages are the next level down, and partials are the lowest level.
A layout page is normally like the header and footer of a page that is common across pages, the content page is the portion that’s different (e.g. about page details, home page details, etc.), and partials are like menu items or other items that may be common across multiple pages.