Either click on the buttons, or press r, s and t to rotate. r rotates through the center of opposite faces. s rotates through the center of opposite edges. t rotates through opposite corners. See notes for a description of what this represents.
This project shows how rotations of a cube is the same as the permutation of 4 objects. The vertical bars are associated with the top of the cube from front left, front right, back right and the back left. As you rotate the cube the bars will move accordingly. It is possible to get the bars in any order you want.
