There are two basic forces acting on a prop. Aerodynamic Turning Moment (ATM) and Centrifugal Twisting Moment (CTM). ATM is due to the relative positions of the C of P and of the pivot point of the blade and will tend to coarsen the blade, CTM is due to the distribution of the mass of the blade and will tend to fine it. CTM is the stronger of the two, so left to itself a prop will fine off (and overspeed).
Most VP props use hydraulics to move the prop, combined with a mechanical governer. A double acting prop has a piston which drives the prop to coarse or fine when required. If the hydraulic supply fails, the prop will go to fine, overspeed and cause drag, so needs a protection system - usually a speed sensing system controlling a mechanical lock.
A single acting system is designed to "relax" to coarse (either by a big spring or by putting counterweights on the blades so that the CTM now drives to coarse) and is driven to fine by a piston which only pushes one way, again controlled by a mechanical governer.
If you want more power, push power levers forward. More fuel to engine, engine speeds up, governer senses it and drives prop to coarse to maintain speed. Unless you have an Astazou engine in which case moving the power lever moves the blade first, engine slows down, governer senses and puts in more fuel to maintain speed - it's a weird system, but it works well. some a/c use this system on the ground (eg C130).