Welcome to an interior page
In Apostrophe, a Page is a type of document that fits into a traditional hierarchical page tree structure. You can see all of the Pages of your site and their relationships by clicking the Page Tree button in the Admin Bar above.
Pages, Areas, Widgets, and Pieces are the common building blocks of an Apostrophe site. For a full glossary of Apostrophe terminology, see our Developer Documentation.
Try creating a new page by clicking the purple Quick Add Button in the Admin Bar. From the New Page modal, you can configure the page properties then either publish and view the page right away or save it as a draft.
A page can't do much without editable elements on it, so we should also take a look at an introduction to Areas and Widgets.