If you open the template from your template manager after installation, the 3rd head that you will find is "Main Menu Settings". Main menu is the standard Joomla Menu Module which you have published at module position - menu.

As you can see in the attached screenshot it has four options. Lets discuss them one by one:

1. Load VM Category Menu: This options allows you to load VirtueMart Categories to the Main Menu module of the site. To enable this feature your will first need to publish VM Category Module at module position - mega-menu from your Joomla Module Manager.
2. Load VM Menu after Main Menu Item Number: This allows your to set where exactly you want to start loading the VM Category Module. For example refer to our demo site. In the demo site the Main Menu has there parent items example - (1) Home, (2)  Our Brands and (3) Explore. We want to load the VM Categories after Home menu item. So we have set this to 1 which means load VM Categories just after the 1st menu item in main menu. 
3. Default Number of Columns in Mega Menu: This refers to the number of columns that you want in your mega menu. Number of columns for VM Categories will also follow the same. 
4. Pull Right Last Menu Item: This allows you to align the last top level menu item to be aligned at extreme right. In our demo site the last menu item is "Explore". After enabling this feature this menu item has been aligned to the right.

Refer to the below image for better understanding. 

To learn more about Hybrid Mega Menu please visit the tutorial page: Click Here