Exactly the same way as the middle layers. A motor rotates each outer layers. On the other hand, the complicated thing to understand is that the cube has 6 oute

Exactly the same way as the middle layers. A motor rotates each outer layers. On the other hand, the complicated thing to understand is that the cube has 6 outer layers (left, right, front, back, top, bottom). But in this kinematics, only 3 outer layers move (left, front, top) and the 3 others remain fixed during the resolution, hence the fact that we see the fixed corner common to all these 3 fixed layers. If the algorithm calculates that we must move a fixed layer, the 3 others will move in the other direction. That's why, although it's a 4x4x4 cube, there are 3 motors per dimension, so 9 motors in total.