In Drupal Commerce, How to generate order using “Add to Cart” button in Custom PHP page

In Drupal Commerce Kickstart, I used custom PHP page in Drupal root folder. As per the requirement I choosed custom PHP Code to show products in different logic pattern. I am getting product id value for each product in that page. Now, I need "Add to cart" button which should generate order number and redirect it to checkout page directly. Please suggest.

Posted: Aug 10, 2013