Categories are a tool used to organize posts and create easy link to the content on your site. To create a category follow the instructions outlined below.
In the Wordpress Dashboard select Posts and at the bottom of its menu select Categories.
Enter the Name that you wish appears on the site.
Also add the Slug which is the url address for the category you are creating. You can add as well the description and assign it a position to a Parent which would make it a Sub-Category.
For more details and information see also: http://umwdtlt.com/wordpress-basics/#organizing-content-with-taxonomies and https://codex.wordpress.org/Posts_Categories_Screen