Nested templates let you create variations of a base template. You can nest multiple templates to define increasingly specific layouts.
By default, all editable template regions from the base template pass through the nested template to the document based on the nested template. That means that if you create an editable region in a base template, then create a nested template, the editable region appears in documents based on the nested template (if you did not insert any new template regions in that region in the nested template).
In the Assets panel’s Templates category, right-click (Windows) or Control‑click (Macintosh) the template you want to create a new document from, then select New From Template from the context menu.
Select File > New. In the New Document dialog box, select the Page from Template category, then select the site that contains the template you want to use; in the Template list, double-click the template to create a new document.