Purchase a 1/8 inch-to-RCA adapter cable from your local electronics supply store, or from your preferred online retailer. The prices of the these cables vary, depending on length you require for connecting your particular multiple devices to each other.
Plug the 1/8 inch end of the adapter cable into your audio source device's "Headphone Output" jack. The headphone output jack may be labeled accordingly, or have a headphone icon next to it. Refer to the device's instructional manual for identifying the jack properly if you are unsure of its location.
Connect the RCA ends of the adapter cable to the second device, such as a stereo receiver. Plug the white (left) male connector into the white female jack, and the red (right) male connector into the red female jack on the RCA "Input" port. The audio coming from the headphone out jack will now be routed through the inputs of the second device.