Not all speakers work in a LD 220 Surround sound receiver

To whom it may concern,
only 2 speakers work and the subwoofer. there is 2 lights in front of the receiver indicating L and R plus a big speaker, ( i am assuming it is the subwoofer) light on. What does it mean I have an additional 3 speaker not connected . Center, right and left rear, they dont work. I have tried to connect the wires but do not work. do I have to connect all the speakers? Please help.