Propeller is All About the Pitch

Essentially, the Propeller is Just a Rotating Wing. Propeller splits the turning moment of the engine into two independant forces: lift and thrust, which causes drag.
The pitch of the propeller is measured from the lateral plane (rotational surface) and the line connecting leading and trailing edge of a blade.
If we start to increase forward speed of the aircraft, it will take higher propeller blade angle to maintain the same angle of attack, increasing airspeed increases angle of attack, therefore, requires higher pitch.
Now we know that fine propeller pitch is mainly for climing and course blade angle for cruising.