Assuming your products have text descriptions already, and you'd like to programatically include those descriptions in the meta description tag, here is my normal solution using the Yoast SEO plugin:
- Navigate to Admin > SEO > Titles & Metas
- Switch to "Post Type" tab
- Scroll down to find "Products" and then "Meta description template" under "Products"
- Fill in the text area for "Meta description template with "%%excerpt%%"
- Save Settings
This will pull the excerpt of the product description and use it as the meta description on every product.
Alternately, you can over-ride the programatic description by editing individual products and setting a custom description.