Well, assuming it is indeed an S-76 we are talking about, I'm pretty sure there is no mast-shortening going on. Beyond that, I am not real familiar with their flight control system in specific terms. I can offer some generalities and some speculation.
Picture the entire rotating set of main rotor blades as a disc. As has been mentioned, the pilot has two controls over the blades in that disc, and, in effect, the disc itself.
Collective the lever on the pilot's left, which includes a twist-grip throttle changes the pitch of all blades equally and (rather automatically these days) increases engine power at the same time. Pulling collective increases the overall amount of lift being produced by the rotor disc.
Cyclic the 'stick' being held in the pilot's right hand angles a swashplate, usually on the main rotor mast to translate that angle to the entire rotor disc at onc. The swashplate is the place where the pilots simple push-pull/ fore/aft left/right cyclic control inputs get converted to rotating push-pull throughputs to the blades themselves. Push forward on the cyclic and through rotating and non-rotating linkage, the main rotor disc angles forward.
The significance of being able to do this is that the net lift generated by the main rotors is perpendicular to that disc. Angle it forward and the helicopter will not only be lifted but pulled forward. Collective pitch increases (with accompanying power increases) will lift the thing in the air. It will then move off in any direction you angle the main rotor disc.
If I am sitting there idling on the ground with the main rotor spinning, I may choose to angle the disc in one direction or another. So long as I do not increase collective ("pull pitch") there is no inherent harm in doing this. If I have people boarding from the right side, I may want to angle it left to increase the distance off the ground of the right side of the rotor disc. In the absence of a specific need like that, I may want to keep it pretty much horizontal to maximize the ground clearance all the way around.
When I am going to lift off to a hover, I want it pretty much dead level else the thing will roll, or take off in the direction of tilt. When I come to a hover the disc should be level - or angled ever-so-slightly into the wind to hold me stationary. To move off forward I will put the cyclic forward which will angle the whole rotor disc slightly forward, and I will increase power-collective at the same time. This will require inputs to the tail rotor through the anti-torque pedals but that is a whole other discussion. (Think Newton's third law of motion)
So if the movement you are inquiring about is a tilting motion, and if this has not fully explained it, could you please be more specific in your question, using up/down - left/right - forward/aft etc.
Happiness is not seeing another trite Ste. Maarten photo all week long.