The Meta Tags that you enter when adding/editing a product or a category will be written to the corresponding category or product page in your storefront only if the file include-metatags.asp is used in pc/header.asp. Make sure that pc/header.asp does not contain hardcoded meta tags (or you will end up with duplicate tags).
If someone else created the file header.asp for you, you can check whether ProductCart is able to writing meta tags dynamically to the page by simply visiting your storefront and moving from one product page to another: does the title of the browser window change? That’s the text at the very top of your browser window. If the title changes, then header.asp has been properly configured.
If you have a large number of products and/or categories and cannot write Meta Tags for each for them, don't worry. ProductCart will dynamically create the Meta Tags for you by using the product name for the Title tag and a portion of the product description for the Description tag.