Most of this comes straight from the tutorials at http://micropython.org/doc/tut-contents.

micro-python-hacking.py

# On OSX
# Connect via USB, open up Terminal, launch interactive REPL to Micro Python
$ screen /dev/tty.usbmodem*

# You'll get a prompt
Micro Python v1.0.1 on 2014-05-12; PYBv1.0 with STM32F405RG
Type "help()" for more information.
>>>

# Play around with the LEDs
>>> myled = pyb.LED(1)
>>> myled.on()
>>> myled.off()

# Flash all the LEDs
>>> leds = [pyb.LED(i) for i in range(1,5)]
>>> leds
[<LED 1>, <LED 2>, <LED 3>, <LED 4>]
>>>
n = 0
while True:
  n = (n + 1) % 4
  leds[n].toggle()
  pyb.delay(50)
# Do a CTRL-C to end the loop