Extension of the template files can be anything. It is recommended [.tpl] for clarity.
PHP source
<?php
// Load class
require_once('OnePlate.php');
// It defines an array of variables to be assigned to the template
$assign = array();
$assign['sample_echo'] = 'Hello World';
// Create an instance
$op = new OnePlate();
// Assign variables, Render HTML
$op->render('sample.tpl', $assign);
?>
Template source (sample.tpl)
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
</head>
<body>
<div>variable is {{ sample_echo }}</div>
</body>
</html>
variable is Hello World