All the templates for your site are located in site/templates. You will find a default.php in there, which is used for every page without a specific template.
If you already read the chapter about adding content you might remember that the content file for the homepage was called home.txt.
Let's say we want to build a specific template for our homepage. All we need to do is to add a new home.php file to the site/templates folder and define our specific html for the homepage there.
This makes it very easy to create your own templates for any page without any further setup. As long as you don't add a page-specific file, the default.php will be used.
To use the same template for other pages, just give the text file for that page the same name.