Oh boy are we going to get this one started or what?!
(1) When power/drag is available and variable, power/drag controls airspeed and pitch controls vertical speed.
(2) When power/drag is fixed, pitch controls airspeed and God controls vertical speed.
Case #1 happens when you begin your takeoff roll, in cruise flight (regular or slow cruise), during descents and on approaches and after the landing.
Case #2 is more evident during your climb, when the engine fails and during a descent when you've already got power off and all the drag deployed.
There are, of course, hundreds of variables and variations which must be dealt with on an individual basis. I'll spare the minutia.
Good luck nailing this one down!
...and above all,
FLY SAFE!
WileyP