Go TO Dashboard and create some Page/Categories/Post
click here for details
Go TO Dashboard>>Apperance>>Menus
and Type Menu name and click on Add Menu
Add all Pages/Categories/Post
This theme support one of the best features of a menu that is Mega Menu. MegaMenu is useful if you want to show posts from specific categories inside the menu. MegaMenu will show the recent posts from the selected category and subcategory in the menu when you will hover it.
Go to Appearance >> Menus.
Create Menus as usual. Place Your Desired MegaMenu Category/Post/Archive link as TopLevel Menu.
And make MegaMenu for this Menu item.
If you want to Add sub Categories for this MegaMenu then,
Go to that Category Admin Page (Posts > Categories Screen) and Click the Edit link of the Category to make subcategory.
This process describes by following images.
Mega menu with sub-categories:
Create Categories and Sub Categories
After that, you need to create a post with subcategories
Then:: Set Any menu item to MegaMenu And Choose any category to make Mega Menu item
Dashboard>>Apperance>>Menu>> Select Menu which is set as the Main menu.
Follow the following image instruction and click on save menu.