How does the 'Show menu button' feature works?

The 'Show menu button' allows you to  display  the currency menu button for currency converter on the store.

To configure the disply of the menu button, please use the following section called Menu button, from the app dashboard preferences page. 

There you can enable it easily by selecting the "Show menu button" checkbox:

When the option is enabled, the menu button will be displayed on the store which will enable an option for buyers to change the currency using that button. 

Most free themes are supported so there is no need to configure anything else. However, customised themes or non-free themes from the Shopify Theme store may require manual placement.