By Default Une Boutique has 4 menu locations, one of the is only available when header style 3 is set as the default header style.
To set the menu positons, on your wordpress admin browse for Appearance → Menus, click on Manage Locations tab and set the menu postions just like the image below and hit save:
To get the 4th menu location to work you have to go to Appearance → Theme Options and on the general tab and under Header Layoutchoose Header V3 and save the options.
When header v3 is selected the new menu location would appear underneath the main nav:
There you go, you just had a sneack peak of the header styles too :)