Menus
The theme supports various menu styles and locations. You can set it in Appearance > Menus > Manage Locations section. See the location of menu areas on the screenshot below:
You can assign a separate, pre-created menu to any of the locations. For showing any locations on your website, Go to Theme Options > Header > Header and add Menu elements and choose location.
Adding icon to menu items
The theme supports icon for each menu items, Go to Appearance > Menus and edit menu(s) that you want to add icon, then like below shot Choose your icon.
If you want to keep only icon without menu label/title, then check Only Icon option.
Mega Menu
See this 3 minutes video tutorial to learn how mega menu works. Mega menu drop down design is according to your imported demo or your changes on menu drop down settings.
OnePage Menu for a Specific Page
If you want to have one page menu with scroll to anchor feature, Then go to Appearance > Menus and create a new menu then assign it to OnePage Location
Then go to Pages and edit your page that you want to have OnePage menu and from page settings, Check OnePage menu
Please Note: in OnePage menu feature, your menus URL should be have like this #section_about