With the overrides system you create a new directory in the includes/templates directory. In that directory copy over the template_info.php from the template_default and open it and edit it to reflect your template name, copyright info, etc.... Go admin>tools>template selection and click edit and select your new template. The directory structure in your new template should be the same as the default template. Only copy over and edit those files that need to be changed for your template, leave the rest alone.