In this theme you are able to display menus in the top bar (Top Menu), header (Primary Menu) and bottom bar (Bottom Menu) (see fig. 1.):
(Note that as in standard WordPress themes, menus can be displayed via widgets)
You can create and assign these menus in Dashboard > Appearance > Menus (fig. 2.)
Custom menu can be created/managed in a usual way. More detail are available here: http://en.support.wordpress.com/menus/
The7 theme supports Mega Menu functionality. Details on it can be found here.
Also you can select position of menu in top and bottom bars from Theme Options.