Step 1: Go to Appearance > Customize > Menus > Menu Locations and use the Secondary Menu select box to choose Secondary Menu. If you did not imported the demo content, you will have to create one at Appearance > Menus.
Step 2: The first level elements of the Secondary Menu allow a Background Image and a Description. If you can’t see the Description field, click on Screen Options, at the top right corner of the screen, to reveal the top panel and check the Description box to add it in the options.
Please note, to be able to display the background image, the secondary menu element needs to have sub-elements.