It's a much more advanced way of displaying your website in HTML. The easy thing about it is that you don't need to type like any html, you can used functions and stuff. Here is an example of how a template class can be used(VERY VERY SIMPLE AND BASIC);
$template = new template;
$template->setTitle("YOUR NEW TITLE");
$template->makeBox("Box Title","Box Content");
$template->display();
In a templating class, you basically only need 1 echo, and that's in the $template->display() function. AND, you can change the title and page information in the middle of the script, unlike some other situation where the <title> was already echoed, so it's too late to change it.