In addition to the 4 hard top and bottom sections on the layout (outlined in the separate top/bottom section articles), you can assign up to 4 additional top and bottom sections.  All the default section options are supported. 

These two custom fields in the sections module are only used for the mobile view of the Hub Template:

Hub Navigation Icon - assigns the icon to the mobile navigation link for the bottom sections.

Hub Navigation Image - assigns the image to the mobile navigation link for the top sections.