“Product description” is an element created for the WooCommerce product single page. This means that you need to use this element only in templates made with the theme builder that are applied for the WooCommerce product single page
There are two types of descriptions, the long description and the short description (excerpt)
The short description
You can add the short description from WordPress here
and the long description from here
Useful Tutorial on how to create a WooCommerce Product page
