The days of the meta keywords field's usefulness have long since disappeared after years of abuse and keyword-stuffing. The meta description field can still be useful as it is displayed in the search engine results pages in search engines, though. Drupal Commerce doesn't give products description fields by default, so you will need to install a module to achieve what you are after.
The following example shows the first result for the search term richard carter, web designer in Google. Below the page's title and the URL, you can see that part of the page's meta description at the time of writing is used as the page's description:
Similarly, in Bing, the meta description of the page is shown in the search engine results page too:
Download the Meta Tags Quick module from Drupal.org at http://drupal.org/project/metatags_quick, and install this to your Drupal Commerce installation.