You put a multiple output soundcard into your PC (usually between 8-10 outputs is good) and you route the sounds you make in your PC to different outputs of the sound card. Then you plug these outputs into some of the channels of a mixing desk. Also, if you have any keyboard, you plug the output of the keyboard into some of the other channels on the Mixer. Then you mix the sound of them all together using this mixer and send the output of the mixer to an amp with speakers attached. You can also record this output back into the PC using the soundcard INPUTS if you so wish.