Hello,

if you used a desktop template like Gantry without a real menu module you need simply to create a new default Joomla module for the site menu and assign it for example to the position 'responsivizer_mainmenu'

It will be rendered automatically as a mobile menu by Responsivizer.

In the pdf section 'Mobile menu positions and management' you find detailed explanations about menu of Responsivizer and template positions.

As a side not, if your Gantry template has module assigned to its own template positions, you can quickly map them to the Responsivizer ones using the 'Positions associations' feature.

Greetings,

John