The following documentation explains the configuration options of the VP Prime Offcanvas Menu module for VirtueMart.
Module Configuration

Select Menu
Select a menu in the list.
Base Item
Select a menu item to always be used as the base for the menu display. You must set the Start Level to the same level or higher than the level of the base item. This will cause the module to be displayed on all assigned pages. If Current is selected the active item is used as the base. This causes the module to only display when the parent menu item is active.
Start Level
Level to start rendering the menu at. Setting the start and end levels to the same # and setting 'Show Sub-menu Items' to yes will only display that single level.
End Level
Level to stop rendering the menu at. If you choose 'All', all levels will be shown depending on 'Show Sub-menu Items' setting.
Sub-menu Items
Expand the menu and make its sub-menu items always visible.
Menu Item Configuration
You can configure offcanvas menu options in the menu item settings under "VP Prime - Offcanvas Menu" tab.

Merge VirtueMart Categories
If prepend, VirtueMart categories are prepended before this menu item. If append, VirtueMart categories are appended after this menu item. Just so you know, the categories will also follow the above layout style for its sub-category items.
Parent Category
Select the parent category whose children will be merged. If top level category, all categories will be merged.
End Level
Level to stop rendering the menu at. If you choose 'All', all sub-categories will be shown.