Drag the cube or move the sliders to rotate the cube. The "z rotation" rotates on the Z axis, which goes front to back. (X axis goes left to right, and y axis goes up to down.) FOV stands for field of view, which is how zoomed in you are.
I was learning about 3 dimensional shapes on Khan Academy, and decided to try it on Scratch. I got all the complex trigonometric equations from Khan Academy (and I understand most of it).