I understand the explanatory form -nda, but why do some phrases end with "nanda" (not to be confused with "what?")? The na is what I don't get.

It's the same structure as "-noda/-nda", but you have to put "na" before it when it follows a noun.

Or a present tense 'na' adjective as well I think (though the 'na' is already there in the first place).

Thanks.