<<QNH refers to an Altitude (amsl), QFE refers to a Height above a specified datum >>
Not strictly correct. Both refer to altimeter settings which produce certain altitude/height readings. Very basically, if the QNH is set on an altimeter it reads aerodrome elevation, ie distance above sea level. Set QFE on an altimeter and it reads 0 (zero) on the airfield, although on some hilly airfields different QFE readings may be produced for different runways. There is a lot of good information here:
Altimetry in general explained | IVAO Academy