The featured category is meant to set an introduction category that helps to identify the topic of a post. The plugin adds a metabox in the edit page of a regular post for selecting the featured category. Note that a small coding is required to display the featured category in the right location of your template. You can display the featured category in the desired location of the page with a set of functions that you call from your template. The plugin CMB2 is required for creating metaboxes.
the_featured_category() takes the current post or page ID and outputs the featured category.get_the_featured_category($post_id) has one optional parameter (post or page ID) and returns the featured category as a string.has_featured_category($post_id) has one optional parameter (post or page ID) and checks whether a featured category exists.