diff --git a/stepper.py b/stepper.py
index 0c43682..d0e28f3 100644
--- a/stepper.py
+++ b/stepper.py
@@ -1,9 +1,20 @@
 # Stepper Motors on Raspberry Pi
-from gpiozero import OutputDevice
-from time import time
 
+from time import time
+from gpiozero import OutputDevice
 
 class Stepper:
+    """
+    Class to control a stepper motor connected to the GPIO pins.
+
+    Args:
+        number_of_steps: The number of steps per revolution for the motor. If
+                         the value is given as the number of degrees per step,
+                         then divide 360 by that number to get the number of
+                         steps (for example, 360 / 1.8 gives 200 steps).
+        motor_pins: The GPIO pins to use to control the motor.
+    """
+
     def __init__(self, number_of_steps, *motor_pins):
         self.step_number = 0
         self.direction = 0
@@ -29,9 +40,31 @@ def __init__(self, number_of_steps, *motor_pins):
             self.pins.append(self.motor_pin_5)
 
     def set_speed(self, speed):
+        """
+        Sets the speed of the motor. This does not move the motor, just
+        specifies how fast it moves when you call `step()`.
+
+        Args:
+            speed: The motor speed in rotations per minute (RPM).
+        """
+
+        # Convert the speed to delay in seconds
         self.step_delay = 60.0 / (self.number_of_steps * speed)
 
     def step(self, steps_to_move):
+        """
+        Make the motor turn the specified number of steps. The speed of the
+        steps is determined by the most recent call of `speed()`.
+
+        Note: this function does not return until all the steps have been
+        completed, which could be a long time for a large number of steps (or a
+        low speed).
+
+        Args:
+            steps_to_move: The number of steps to turn. A negative value turns
+                           in the opposite direction.
+        """
+
         self.direction = 1 if steps_to_move > 0 else -1
         steps_left = abs(steps_to_move)
         while steps_left > 0:
@@ -46,20 +79,24 @@ def step(self, steps_to_move):
                     self.step_motor(self.step_number % 4)
                 steps_left -= 1
 
-    def step_motor(self, cur_step):
+    def step_motor(self, cur_step: int):
+        """
+        Internal method to implement a single step by toggling the GPIO pins.
+        """
+
         if self.pin_count == 2:
             if cur_step == 0:  # 01
-                self.motor_pins[0].off()
-                self.motor_pins[1].on()
+                self.motor_pin_1.off()
+                self.motor_pin_2.on()
             elif cur_step == 1:  # 11
-                self.motor_pins[0].on()
-                self.motor_pins[1].on()
+                self.motor_pin_1.on()
+                self.motor_pin_2.on()
             elif cur_step == 2:  # 10
-                self.motor_pins[0].on()
-                self.motor_pins[1].off()
+                self.motor_pin_1.on()
+                self.motor_pin_2.off()
             elif cur_step == 3:  # 00
-                self.motor_pins[0].off()
-                self.motor_pins[1].off()
+                self.motor_pin_1.off()
+                self.motor_pin_2.off()
         elif self.pin_count == 4:
             if cur_step == 0:  # 1010
                 self.motor_pin_1.on()
@@ -144,5 +181,9 @@ def step_motor(self, cur_step):
                 self.motor_pin_5.on()
 
     def stop(self):
+        """
+        Stop the motor by setting all the GPIO pins low.
+        """
+
         for pin in self.pins:
             pin.off()