Erm, go library and start looking? Online and start googling for stepper motor controller?
Anyway, first you need to know what type of stepper motor (unipolar, bipolar, their circuits are different), what is the rated voltage and current (so you don't burn them).
Stepper motor operates by constantly changing the supply voltage on their teminal.
They are for very precise control, some are rated up to few degree. You need to know how many steps to make 1 turn cycle. Speed control are done by applying time delay between each pulse. It's not exactly a good idea to use stepper motor to control speed, you will see pulsation jerking especially at low speed.