There are four places within an OpenCart admin area where you can add SEO related information: categories, products, information pages and your general store settings. Most fields are located in the general tab, data tab or SEO tab depending on the version of OpenCart you're using. These make up the vast majority of pages which you'll have on your website. For any other pages, for example the contact page or register page, you'll need to get a web developer to add custom fields to your admin area or directly add the meta data straight into your website's code. If you'd like a hand adding the meta data to these pages just get in touch and our team will be happy to help.