There are 3 reasons why a category may not show on the menu:
The Category is not marked as available
Make sure that the category is marked as available in the dashboard
The Category does not have any items in it
In order for a category to appear on the website, it has to have at least 1 available item within the category
The Category was not added into the actual menu
In order to add the category onto the menu, go to Dashboard > Restaurant > Menu, and click on the menu you'd like the category to be in
Click on Add Categories and select all applicable categories. Click Add Categories+
Click Save Menu