It would help to know what motherboard and case you have to give specific instructions. The one labeled USB goes to the onboard USB sockets. Be careful. If your case and MB have Firewire connectors, keep in mind that they are keyed the same as USB and mixing them up can damage the motherboard. The narrow connector looks like audio. Many cases include both HD audio and legacy audio. Modern MB's use HD audio, so if the HD is already connected, then the legacy connector does not get used. Just tuck it out of the way.