Template files are what Drupal uses to determine how to render the HTML for a page. When you wish to create a custom theme, there are several files you will likely include in your theme's directory:
- page.tpl.php - this controls the overall look and feel of your site (slight change for Drupal 7). For those of you who have coded sites with HTML (and CSS), this is like the index.html page you created.
- node.tpl.php - this controls how a node is built