bulldog89
In the cruise it's quite simple: Pitch controls altitude, thrust controls speed. Auto or manual thrust is irrelevant.
VNAV in a Boeing is a complicated beast and understanding the FMAs as they change is vital. Pitch can be used to control Speed, Altitude, Rate of climb, Flare etc.. Whilst Thrust can also be used to control Speed, Altitude, Rate of climb etc - the only difference being the phase of flight.
It's a subject that (in detail) belongs in a type rating course, not the ATPLs.