I don´t know which Mb or graphic card you have. Anyway the only necessary cables to connect to your graphic card is a 8pin power cable or eventualay another 6/8 pin power cable if you have a monster GPU that connect directly to your Power Supply. But many graphic cards don´t need anything connected to them. Just insert it firmly in the slot, screw the screw(s) on the back of the case and you´re set.
That spdif cable is an audio cable in case you want sound to go through your graphic card. If you connect it to a TV for example. For a normal monitor you don´t need to connect anything unless it needs extra power.