Traditionally, orange, green and black TRS cables are used in 5.1-channel audio applications. The orange cable carries the center and subwoofer channels, the green cable carries the front left and right channels and the black cable carries the rear left and right channels. Connecting your orange, green and black audio cables to the corresponding outputs of a 5.1-channel audio source will deliver the sound profile your speakers were intended to produce. However, if your source only has one audio output, you'll need to combine the three cables in order to get sound out of all the speakers.
Purchase two adapters: one to combine your 5.1 signal into left and right RCA signals, and one to convert your left and right RCA signals into a single stereo TRS signal.
Plug your orange, green and black cables into the TRS-to-RCA adapter.
Plug the second adapter into the first, converting the two RCA signals into a single TRS stereo signal. This second adapter can now be plugged into the single audio output of your computer or small electronic device.
When you combine your three audio cables into one and connect them to a mono or stereo source, you will hear sound out of all your speakers, but it will not be true 5.1 surround sound.
If you plug only one of the cables—orange, green or black—into the single audio output of your source, you will hear sound only on the two corresponding speaker channels.