Wanna stack? This tutorial shows how to use the plain header to connect to an Arduino. If you want to use stacking headers, don't follow these steps!
This step is for all Arduino and compatibles. Please note that we use the hardware SPI port (the 2x3 pins) for talking to the Bluefruit LE module. If that port is not available you'll have to jumper the SCK/MOSI/MISO pins to other pins and use 'software SPI'!
Begin by breaking the 36-pin male header into four pieces: one 10-pin, two 8-pin and one 6-pin. Stick the header into the Arduino sockets with the long pins down.
Also place the 2x3 female socket header into the ICSP header on the right of the board
Place the shield on top so that all the little pins stick out through the matching holes in the shield. It should match up perfectly!