We might divide a page template into a header, content, sidebar and footer where these are in separate files. The content will change most between pages, so rather than having a content file, we include the content into a page file which pulls in the individual template files and defines the unique features of that page. The unique features of a page will be the title, description and article content. We can define these at the start of the page template with say PHP code to set the value of variables that are used by the other templates such as the header template. Then we assemble the page by including the required templates and inserting the content.
If we directly insert the content, we will create a new page template for each page of the site. But this is fine since we are not duplicating the header, footer and sidebar. To reduce the number of page templates, we can store our content in a database and use a page ID to identify which page content to insert. This ID is usually appended to our URLs of the website. If we do this, we are creating what is known as a Content Management System (CMS). Where the theme is likely to be changed often or people are encouraged to design new themes, a separate directory can be created to hold the various themes. A read me file could be included to credit the designer, or this information could be added to the start of the style sheet as a comment section.