Before write content article for blog post, or for static page, for first make sure you have create categories for your content article, this is for grouping your blog post or static page content article.
Access on your backend admin, and visit on categories, now you can see all categories list , for edit you can click on edit menu, for delete you can click on delete menu.
If you want to create new categories , so you can click on + add new categories button. then insert categoy name and description, after that save it.