A: Secondary fields should only be used for bilingual menus (when there are two languages present). 

More specifically, for U.S.-based restaurants, the secondary fields should be used for the non-English language.

Secondary fields can be used by adding the same field twice.

As shown in the above image, the "Title" field was added a second time to create a secondary title field. Likewise to create a secondary description field, you just have to add a "Description" field again. 

There is no third field.

Incorrect use:

As you can see above, the Spanish description was put in the primary description and the English in the secondary description.

Correct use:

Because this is a U.S.-based restaurant, the English translation should be put in the primary description and the Spanish in the secondary.