Building a Neapolitan sixth chord is easy.

We begin with the tonic chord (A minor in this case):

Build a major triad one diatonic half-step or minor second above:

Set the chord in first inversion:

Double the lower note (the third) and we get the Neapolitan sixth chord:

To identify a Neapolitan sixth chord, remember that it is a major chord, usually in first inversion, a half-step above the tonic chord.