Features can be very useful as you can assign a unique set of FEATURES to each Primary or Sub-Category.
STEP 1: Go to Listings > Categories
STEP 2: Add select a Category. (To add new category, See How to add a Categoriy?).
STEP 3: Select all the features associated with the category.
If no features are available to select from the drop-down, then you must first add new features. Read How to add Features?