Mega menu is the submenu which display post title along with its feature image in the menu location as shown below. It is available in Premium version only.
How to apply mega menu feature in your website.
Step1. Go to appearance >> customize >> menu
Step2. Open screen options and there you can find checkbox named as CSS classes. Select it.
Step3. Add custom link in the menu and add class name as “mega-menu” in the place defined under ” CSS Classes”. Now add submenu under this menu . Your submenu could be one of the listed below.