Plug in a USB cable connecting your Flora to your computer.
Open the special Adafruit version of the Arduino IDE and naviate to File-->Examples-->Adafruit_LSM303-->Test to open the accelerometer test sketch. For more information on programming the Flora, check out the Getting Started with FLORA
Be sure you have the correct serial port and board type selected under the Tools menu, then upload the sketch to your Flora.
Modify this sample sketch to integrate this sensor into your project. Debugging over USB is helpful to see the ranges of numbers your sensor provides, but once your code is solid, you can disconnect from the computer and power your project with a 3xAAA battery holder.