For example, you might choose to categorize your blog posts as: Weddings, Engagement, Travel, etc. By default, your WordPress account will have only on Category: Uncategorized.
Narrative Publish gives you the option to assign your post to one of the categories that you have defined in your WordPress admin page. Each time you make a post, you can select the category you would like to post to by clicking on the category dropdown found below your URL:

You can update or add new categories within WordPress.