Doing FFT in realtime

I want to do the FFT of an audio signal in real time, meaning while the person is speaking in the microphone. I will fetch the data (I do this with portaudio, if it would be easier with wavein I would be happy to use that - if you can tell me how). Next I am using the FFTW library - I know how to perform 1D, 2D (real&complex) FFT, but I am not so sure how to do this, since I would have to do a 3D FFT to get frequency, amplitude (this would determine the color gradient) and time. Or is it just a 2D FFT, and I get amplitude and frequency?