Before you begin to study the operation of stepper motors you need a reasonable understanding of electromagnetic principles. From this you will advance to an understanding of how DC motors and generators work. If you believe that you are full bottle on this (i.e. you understand these principles) you could skip these sections and go directly to the stepper motor theory.
During the following discussion you will be given the opportunity to view graphics that may explain some concept pictorially. When this happens, and you take advantage of it, you merely access the 'BACK' key in order to resume the discussion. This is done so that you may skip certain graphics if you wish. When an animated drawing is presented in this fashion the animation will go on forever until you press the 'ESCAPE' key.