The best place to read up on the BFD is on the BFD forum at hometheatershack.com. When you power on the bfd it will automatically load the last filter set you had loaded.
The top right button on the bfd is labeled in/out. this is used to turn filtering on (light on) and off. If you want to monitor the input side of bfd rather than the output, you press and hold the button for a few seconds until the indicator light flashes. This bypasses the filters and shows your input levels on the leds on the left hand side.
The input monitoring is used to set your input signal level for the bfd. The recommendation was to set the input signal so that the orange LED (-3db from clipping) barely lights on the most bass heavy material. I used the LOTR Bridge of Kazad Dhum scene to set my levels. I actually backed off one from where the orange light came on. I think that put my subwoofer signal at +4 or 5 on the receiver.
