The program creates a real-time audio feed by using 'analoginput', which is filtered though a band pass filter and the dominant frequency is extracted with FFT and then plotted. I've thought of this script as a voice coach, so I've also plotted a few musical notes as reference on the frequency scale. In theory it is possible to create any reference sequences, which means that one could learn to sing anything perfectly. There are two other plots, the bottom-left one shows the current filtered signal and a bottom-right one shows the frequency spectrum. These plots give a picture to the user of the signal's composition.
Of course this can be put to far better use than singing but that's up to you.