It never ceases to amaze me that people get to fly aircraft and are not instructed on all the equipment therein. Another case of an extremely poor reflection on instructors, training pilots and CASA.
HF like other equipment does need to be understood to obtain the max efficiency out of the equipment and the medium it uses. Too many, it seems, it is all to hard (and is left OFF) and only something that should be used on a rainy day, so you don't need to know much about it till then. Hopefully you will get lucky at the time you need it most!
Of course if you are under instruction you should have asked all these questions at the time?