How to add and edit categories in WordPress
In WordPress you can assign your posts/articles to one or more categories. To add and edit categories, log in to the admin panel and go to Posts menu>Categories submenu. On the page that opens there's a form for adding new categories and a table displaying the existing ones.
The table is divided into several columns. To hide any of these columns or to make it visible again, click on the Screen Options button in the upper right corner of the page and mark/unmark the corresponding checkbox(es). You can't remove only the column for the name of the categories. To delete several categories simultaneously, mark the checkbox in front of the name of each one, select Delete from the Bulk Actions drop-down menu and click on the Apply button. To delete only a single category just hover the mouse pointer over its name in the table and click on the Delete button that appears. A few other buttons show up when you hover the mouse pointer over the name of category. The View button redirects you to the category page on the frontend. With the Quick Edit button you can edit the name and slug of the category. The Edit button will display the edit form with all the category settings.
The add and edit forms are the same. The only difference is that the add form is shown on the page with the table with the existing categories, while the edit form is on a separate page. The form has a text field for the name of the category. That's the name that will appear on the frontend. The next option is Slug. Slugs are used when permalinks are enabled. The category slug is that part of the friendly URL of the category that corresponds to its name (e.g. category-name in yourdomain.com/category/category-name). If you leave the field for this option blank, the name will be used as the slug. For more information on permalinks, check out the tutorial on managing permalinks in WordPress.
On the add/edit category form there's also a Parent drop-down menu from which you can select the parent of the category (in case you want the particular category to be a subcategory of another one). There's also a text area in which you can optionally type a short description of the category. Depending on the theme that you use the description may be shown at the top of the category page on the frontend.
For some more details and screenshots read the tutorial on WordPress categories.