All micro coaxial RC helicopter work the same way. They have two separate electric motors that drive each rotor. Each motor drives a main gear.
At any rate, these two main gears turn two main rotor shafts. The outside shaft that powers the lower rotor is hollow and the inner shaft that powers the upper rotor is spinning inside the lower hollow shaft – obviously in the opposite direction – pretty simple.
These two motors control both the lift of the helicopter by speeding up and slowing down. They also control the turning or yaw movement of the heli just like a tail rotor would on a single rotor helicopter. How?
If one rotor is slowed down a bit, and the other is sped up, the one that is turning faster will produce more reactive torque than the slow one and the heli will turn/yaw, just as if a tail rotor turn command was given.
This yaw movement is controlled by a special electronic mixing board that will seamlessly mix the speed of both the motors to allow the required turn rate while also making sure the overall lift remains the same.