Refer to figure.
QNH: The barometric pressure measured at a reporting station (the QFE) which has been mathematically adjusted down to mean sea level using the airfield's elevation.

• If you are on the ground at an airport and set your altimeter’s subscale to the local QNH, it will display the airport's altitude above mean sea level.

QFE: The barometric (atmospheric) pressure at an aerodrome reference point. Essentially it is the measured surface pressure of the airfield.

• If you set the QFE on your altimeter’s subscale on the ground, the altimeter would read 0 feet.

QNE: The indicated altitude at the landing runway threshold when 1013.25 is set in the altimeter’s subscale.

• In other words, it is the pressure altitude at the landing runway threshold.

QFF: Mean sea level pressure, derived by taking into account the actual temperature conditions.

• So, the QFE reduced to mean sea level with regard to the actual outside air temperature.