To add new pages, go to the vertical management bar on the left side of the editor and click on the "Pages" tab.
The pages of your site will appear in the site's navigation menu and be displayed in a list.
If you need to create a new page to be placed as a subpage, first, click on the + New page button.
Whether the page is new or already existing, you can create a subpage by dragging and dropping it to the right.