See the Bitlash documentation online at http://bitlash.net.

Quick Start: 

As of Arduino version 0015 and later, Bitlash is provided as an Arduino Library.

To install Bitlash, unzip the download and copy or move the bitlash distribution folder
into your Arduino application's "hardware/libraries" directory as "/hartdware/libraries/bitlash". 
(You will need to rename the resulting folder to simply Òbitlash" to remove the version number.)

To use Bitlash, open, compile, and upload the "bitlash-demo.pde" sketch, which you will find 
in the hardware/libraries/bitlash/examples/bitlash-demo folder. 

Then connect via the serial port at 57600 baud and off you go.