The fans built into the graphics card? They get their electricity from the PCIe slot (or perhaps the PCIE cable, not sure).
Plug in the card, connect the 6 or 8 pin PCIe from the power supply to the graphics card female slot. Start the system and it should work. If your power supply lacks the 6 or 8 pin male PCIe connectors, you may need to upgrade the power supply.