Ecommerce categories are setup from Sales/Configuration/Product Variants (?!?)/ Public Product Categories - this only defines the structure of the categories - there is no ability yet to add description or content as yet.
As pointed out here:- https://www.odoo.com/forum/Help-1/question/Category-content-on-webstore-55062 despite Odoo's target of being able to edit all website content from the front end at present shop/category/keyboards and shop/category/monitors all generate the same webpage so keyboard specific content placed here will appear on monitor pages also (and vice versa) - we have to hope that this is changed soon or there will be no way to describe individual categories to users, optimise for SEO, show beautiful images, drive sales through marketing different categories in different ways, etc, etc.
Some feedback from Odoo on this point would be most helpful.