Mine was was split into two halves. The first was in the 'classroom' where I was tested on my knowledge of the information in the aircraft manual - eg. engine bhp, type of oil to use, type of fuel & colour code, MTOW, BEW, type of brake & steering system, etc. We then went out to the a/c and the FE asked me to explain the principles of flight, and the function of certain parts of the a/c, eg/ pitot tube & heater, ailierons, static vent, stall warner etc with explanations of the principles behind them, along with type of flaps, types of aerials fitted and what each was for (VOR/radio etc). The whole thing lasted about 45minutes. Beware for trick questions! Overall it was pretty easy-going and laid back, but it depends on the examiner I s'pose.
Hope this helps.