Stereo Headset/Boom Microphone

I bought a Labtec Stereo Headset, but I do
not know how to plug it in my PC. There are
three plugs, in back of the tower box.
They are color coded. But I can not receve
sound in the head set. Do I have to un-plug
the speakers? Do I need to re-set the files?
Do I need a new sound card? If I can only use
one or the other, speakers or headset, at one
time, and then unplug, and re-do, this would
not be right. Can you help me?