That´s the point on the unlabeled look, also it promotes unexpected results when not knowing exactly what you are connecting.
The ps2 keyboard tells the arduino CV/Gate secuencer module what secuence to play, when and how. The letters and numbers are mapped to midi notes, and the other keys have their functions as well. There is also a pot in the panel to control analog changes like playback speed, probability of played notes, and such. I will make a deeper explanation of this when I have it ready to share.