It has 2 slots (for power I think), 1 has 6 holes, 1 has 8 holes, do I need to connect them both?
Power to both sockets are needed, they wouldn't put them on there otherwise. What you can do is buy one of these...
It's 2 molex to 6pin. It's preferable to have the 8pin slot filled with an 8pin plug but this will still work.