Understanding "FFT" Can anyone understand what I have in the picture?
You see a spike. That means this frequency is very much present in your signal. All the other frequencies don't have a spike, but they're still present, though less.

But really, why are you doing fourier transform on a DC level, as KyranF points out?

On Wikipedia, Fourier transform is explained, if that's the problem. This image (from there) may help as well: