How to Add Categories in Joomla 3.x
Using categories and subcategories allows you to structure your articles better. It is useful to group your content and display it in more organized way to your visitors. In Joomla 3.x, first you need to make the categoreies and then assign an article to them. To start, click on the Category Manager link in your Quick Links menu.
On the next page, click on the New button at the top-left part of the page in order to add a new category.
Now, enter a title for your category, a brief description if you want and press the Save button.
Your category is now saved and ready to be used. When you publish new articles, you will be able to choose it for article category. Note, that you can make subcategories, by setting parent of the category, you're currently creating.