By default, WordPress adds a category for your blog posts called uncategorized. It looks crappy and should be changed to something like All or Articles.
In WP Admin, navigate to Posts > Categories. Hover over the Uncategorized category and click on Edit.
In the next screen, enter the category Name and Slug and click update. Make sure the slug is in lower case.
That’s it. You have successfully changed the ‘Uncategorized’ category to ‘All’.