You have to connect the front panel audio wiring connectors to the pins of the device you are using for your sound source. If you are using the onboard sound, there should be a row of pins on the motherboard with descriptions for each pin.
If you are using a soundcard, then you have to find out how to hook up the front panel wires to the card in order to use the front jacks.
If the front panel connector wires have phone plug ends, then its just a matter of plugging them in the appropriate output plugs on the sound source.
The wires may have to be connected via the pins if there is no phone plug termination. Your motherboard sound will probably have pinouts for that type of connection, but a soundcard may or may not support that type.
Al