Usb cables have 4 wires, +5V, data, data, and GND in that order. computer power cords (as in the ones that go from the wall to your PSU have 3, positive negative and ground.
for audio cable if you are making a mini to mini cable you only need 3 wires. Right left and ground. lets say that the 3 wires in your cord are red blue and white. strip both ends and solder the white wire to the ground pin on whatever connector you use, connect the red wire to the right channel pin and the blue to the left channel pin. then simply repeat on the opposite side (making sure you use the same color wire for the same connectors)
