theming – How to print custom fields of a custom product type in my page – product-display.tpl.php file?

I am a beginner in the drupal thematization,
I want to create a special template for the custom page of my product (page – product-display.tpl.php)
I use this php code to make the field but it did not work!


by the way, I have a product type called "product" and also a type of custom content called "product-display".
Should I add crochet things to the template.php file that I do not know?
Thank you.