From Textpattern CMS User Documentation
Presentation > Pages is a basic editor. The page templates used by Textpattern are created in this editor. It's important to note that, like everything else, the page template is stored in the database. This is the primary way of getting at the template and modifying it. There is no physical file on the server that contains this template.
Along the right hand side of the page is the list of known pages. To select a template for editing, click on the name and Textpattern will fill the editor with the selected template. Additionally, the phrase at the top of the box "You are editing page template template name" will change to reflect this.
A Save button, located at the bottom of the edit box will save the template back into the Textpattern database. Additionally, there is a field named "Copy page as:". To create a copy of a page template, enter the new name of the template in the field, and click the "Copy" button. The page will update and the new page will be displayed on the right hand side list.