It is easy to build a Neapolitan sixth chord.

We start with the tonic chord (in this case A minor)...

build a major triad one diatonic half-step or minor second above,

set the chord in first inversion and...

double the lower note (the third) and we get the Neapolitan sixth chord.

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