By default Kart theme will place Main navigation menu in primary menu region.
How To Add or Remove or Disable menu Links
Navigate to: Home > Administration > Structure > Menus > Main navigation
example.com/admin/structure/menu
Here you can manage links of main menu.
How to make Drop Down menu
Kartpro theme has inbuilt feature of Drop Down menu powered by CSS3.
Navigate to: Home > Administration > Structure > Menus > Main navigation
Click Edit button of parent menu link.
Check Show as expanded option of this parent menu link and save.
Repeat this step for all parent menu items.