The Luftwaffe aircraft use variable pitch props. These are not constant speed props (there's no governor) so you directly control the blade angle to influence the RPM. This means that whenever your airspeed, throttle or attitude changes you will also have to make adjustments to the prop to keep the RPM where you want it.
The RAF ones have a lot of different props, ranging from fixed pitch (tiger moth), to two-position props (early spits and hurricanes) to constant speed props.
With a fixed pitch prop, the RPM is controlled by your airspeed and throttle settings. With a two-position prop it's like having two fixed pitch props, one for best cruise efficienty (the low RPM setting) and one for maximum power (the high RPM setting).
Finally, with a constant speed prop you just move the lever until you get the RPM where you want it and it will take care of things on its own from that point on. It's still possible to be unable to maintain the chosen RPM when the blades reach their movement limits, eg you will notice that even with the lever full forward you're not making a lot of RPM when idling on the ground, or in a similar fashion you might be able to overspeed the prop in a prolonged high speed dive.
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