How the systems yaw
Oookay, well someone might beat me to this, but…
Tandem rotor system, like the Chinook:
To yaw, one rotor “banks” left while the other banks right, fuselage pivots in middle. I hear (but have no firsthand experience) that a good Chinook pilot can, through finesse with cyclic, collective and pedals induce the big tandem to pivot around the nose or tail.
Coaxial rotor system (contra-rotating rotors stacked on top of each other), like the Kamov:
To yaw, one rotor increases collective pitch while the other decreases collective pitch. The resulting difference in torque about the rotor driveshaft(s) causes the aircraft to pivot about the rotor mast. The vertical tail surface provides stability in forward flight
Synchromesh counter-rotating rotors (side-by side), like the Kaman:
One rotor pitches forward while the other pitches back, dragging the fuselage around a point between the rotor masts (a lateral version of the tandem, I suppose). Again, the vertical stab provides stability in forward flight.
That's as far as I know, anyway.