Hi Naythan,
QFE is discussed in the Air Law section of the BAK textbook on page 10.21.
QFE is another of the old Q (or Question) codes. QFE stands for "Question: Field Elevation" or in other words, "what is the atmospheric pressure at the field?"
QNH is "Question: Nil Height" or "what is the atmospheric pressure at sea level?" If you set QNH, the altimeter will show your altitude above mean sea level.
So, if you set QFE, the altimeter will show you your altitude above the aerodrome datum. QFE isn't used much anymore - we stick to QNH (or 1013 once you get above 10000 feet).
You'll find info on altimeter setting procedures in the AIP ENR 1.7 (2) and Fig. 1 in that section as well.
If you're interested, here's a link to a list of the old original Q codes:
www.kloth.net/radio/qcodes.php
Cheers,
Rich