Page templates store reusable page content for the original page-creation workflow. They are separate from the website-wide layouts and themes in Website Templates.
Create and Use a Saved Page Template
Open Setup > Website > Page templates, click Add Template, and enter the template name and content.
When using the original page-creation workflow, select a saved template while adding a new page to insert its content into the editor.
Modern Block Builder
With Enable block editor switched on, new pages open directly in the modern website builder. The old saved-template selector is not part of that add-page workflow.
Instead, use Example section layouts in the builder to add editable groups of blocks, such as welcome sections, training information, membership fees or FAQs. Customise the example content and publish the page when ready.