I recently recieved an Arduino Uno, and I need help with an FFT. I don't really understand what it is or how it works. I am trying to use it to take a beat from music, and turn it into somthing I might be able to use for lighting effects. I got pointed Here. I see a lot of code, not sure how to apply it. Please help, Thanks.

I've actually struggled with that exact same piece of code for PartyMode 2 in my bedroom. One of the most important pieces of the puzzle is that you also need a circuit to remove the DC bias from the incoming audio signal and add a DC bias of your own, putting the peaks of the signal between 0V and 5V. For using that code, you will repeatedly push in samples from the incoming audio, and it will give you the frequency-domain signal. In other words, if the incoming audio was a pure 1KHz signal, the FFT would have a single peak at 1KHz. You can use the rise and fall of the FFT at low frequencies to determine the beat of the music.