What is meant by "Control your descent with throttle when landing, not with pitch"
Your pitch is adjusted to maintain airspeed, whereas throttle and thrust are used to establish a rate of descent.

Shameless steal from KeithS comment below:


  [Y]ou're gliding down to the runway, but you need a little engine power to keep a shallow glide slope because you aren't in an actual glider. The real explanation is that trying to use pitch to control glide slope causes dramatic changes in angle of attack, especially at the lower speeds used for approach and landing. This could cause a stall, or a severe loss of altitude. The throttle provides much more minute control over your angle of attack and thus your glide slope.