To add a new Blog Category select the Blog and then Blog Categories from the left hand menu:

Then click on the "+" button in the top right hand corner:

This will take you to the Add Blog Category Page.

The Add Blog Category Page will have many elements. On this page you can turn the active status of this content off or on:

You will enter a title for your Blog Category:

You can also enter a Description that would be displayed with your Blog Category:

Don't forget to save your work by clicking on the Save icon in the rop right hand corner: