After completing the installation process, you will get access to admin panel. From there you can add/remove categories of your shopping cart. To add a product category in OpenCart, log in your OpenCart admin panel and go to Catalog » Categories from the admin navigation menu.
It will open the categories screen.
Click on "insert" button on the upper right corner of the page.
Enter basic information such as category name, meta description, meta key words and description about category. Next, Go to Data tab.
This will allow you to add hierarchy of your categories. You can set Search Engine friendly url for this category in "SEO keyword" field. Also, you can set image for your new category by clicking on "Camera image" and a popup will appear allowing you to upload a picture you like from your local computer or set a pre-existing one which is already uploaded in the images directory of OpenCart.
Category status allows you to disable/enable the category on your site. Sort Order set's the order of which the category will be displayed amongst others in the same parent category. Next, Go to "Design" tab.
Here, you can set your category look and feel. And, Finally you need to click the "Save" button(located upper right corner) to save your new product category.