From the guide it shows you how the cubes and cylinders become one to form the complete form of the character. Subdividing these cubes and cylinders also indicate where certain additions will be added once more detail has been put onto the character. Using straight lines also outlines the perspective and direction the characters body is facing.
A quick orthographic of Mr Fantastic also gives depth to the design and you can definitely tell from the shapes what parts of the body stick outwards and where the figure cuts in. The lines get darker to show where the figure cuts in on certain parts of the body.
The poses are quite dynamic and they experiment with the flexibility to the characters they are used upon. The drawing starts from the most simplest designs with thin shallow lines and then build up into structures and then the final design.