Here's the video guide for Megamenu
Here's the step-by-step text-screenshot guide:
Please follow the instructions mentioned below (For All Mega Menu):
Go to Customize > Sections > Header > Add Content > Mega Menu
Select the URL on which you would like to make Mega Menu visible
Select Menu "Main Menu"
Please follow the instructions mentioned below (For Specific Mega Menu):
Go to Navigation > Create New Menu
Use "#" or "/" under Menu Name
Use "#" in Link Trigger and Select Created Menu
Go to Navigation > Select "Main Menu" > Add '#'