To experiment the bipolar stepper motor with Arduino, many one will use L293 motor shield, unfortunately I cannot find one, I tried to build from alternate parts, luckily we still have the Google God to fulfill our wish, I got the circuit from Wiki, https://en.wikibooks.org/wiki/Practical_Electronics/Stepper_Motors , to build the driver with MOSFET, because I can still find MOSFET in the market.
Step 1: The Circuit Diagram
If you like you can surf the Wiki and find the circuit. as I don't create the circuit, so will not post here. What I've done was the circuit board with the MOSFET, I used 4 N type and 4 P type MOSFET soldered on a small multi purpose circuit board. This circuit required external power supply, do not taken from the Arduino board, but the ground connection does.
Step 2: Connect All Stuffs
With refer to the link https://www.arduino.cc/en/Tutorial/MotorKnob , you can find the code and details, connect the PWM lines to the output pins, the motor coils, and external power (may be sourced over 1 ampere) , remember bipolar stepper motor has two coils with 4 lines, over 4 lines is unipolar stepper motor needs other driver.