To define the products or category Meta tags go to the Catalog -> Categories/Products list.  Click on desire product or category and then look for a symbol, resembling the BMW’s mascot, in the Action column.

meta tag button

After clicking on Meta tag button in Action following page will display up, fill in the details and click Preview, then Update.

 Edit Meta tags and Description

It is important to know that Meta tags and Meta Description need to be relevant to the product entry, otherwise they will not be useful at all.