1) Sets the amount of fuel added to the intake airflow. At higher altitudes the air pressure (and therefore the oxygen level) declines so the fuel volume must also be reduced to give the correct air/fuel mixture. This process is known as "leaning". Too much fuel and your engine can overheat, produce less horsepower and possibly explode. Methane for instance must have a proper fuel air mixture or it won't combust - in an aero engine it has to combust efficiently to produce the most power and not damage the engine. Basically your cordial - water ratio.
2) Radiator allows cold air to cool the fluids (Coolant) in the engine to maintain optimal temperature. Too little heat to start your engine - close the radiator, too hot, open it up or your engine will overheat, boil and you will have oil all over your canopy.
3) Propellor pitch ofcourse affects thrust output being how much air is 'caught' by the blades. More prop pitch, more air is caught = higher RPM, lower pitch = less air caught = lower RPM.
In diving or high speed engagements you will need to lower the prop pitch in order to avoid exceeding the engine RPM limits, if your engine 'over-revs' then it will damage the gears and shafts and you will destroy the shaft.
Atleast this is how I would describe these things.