On page two of every product set up in your Order Management System (OMS), you will see fields to modify the metadata.
You may also modify the metadata for categories, as well, on the category setup pages (the fields look exactly like those above for products.)
While the field for Meta Keywords remains in the OMS to retain data entered by legacy clients log ago, they are irrelevant at this point to SEO, and likely should not be used. We recommend using the Title Tag, Image Alt Tag and Meta Description fields for best SEO results.
For more information on where to add SEO, Marketing and Tracking Code in the OMS, check out this article.