When the card is installed into the motherboard
connect the cable from the back of your pc monitor
to the back of the graphics card
Hopefully your PSU has 2 molex connectors to accept the 6pin/8 pin connector.
If your PSU has a 6pin/8pin connector coming out of it, skip the rest of my post
If it doesn't, read on,
After the 6 pin /8 pin is plugged into the gtx 580, like picture
the other end of the 6/8pin cable needs to be connected to a cable coming from your power supply,
to a cable that looks similar to this
If your psu does not have any, then you may need to atatch them, using an adaptor, of whatever cables are left to use up from your PC, like a
sata to 4 pin molex connector.
take some pics of inside your case and the installation of the card you did.