How to create megamenu

Actually you dont need to create a new one unless you want to use vertical menu, not horizontal one. You just need to add items to default menu (ID =1). 

You can refer our document here: 

https://www.magesolution.com/themes/claue/docs/m2/index.html#create-megamenu-item

Please note: You need to choose the proper store view then clear page cache after making any changes