4+4 or 20+4 or both to power CPU??

The 20+4 pin goes into the one slot on the MOBO for the 24 pin and for the 8-pin you will only use the 4+4 plug into the 8-pin socket (they make it a 4+4 because older MOBOs only have a 4-pin plug and that way you would use the 4+4 pin by plugging in the 4 pin and leaving the other 4 not plugged in (the 4 pin can provide up to 150W but newer CPUs maty require close to that limit so they made the newer 8-pin mobos to support the higher requirements) -- Same goes for the 20+4 as older MOBOs will have only 20 Pins in which case you would use the 20+4 plug and leave the +4 unplugged.

So the pins are made like this so you can use the PSU on either older or new systems. But for your new MOBO you will just use all of the 24 pin (20+4) in the one plug and the other 8 pin (4+4) in the plug near the CPU socket.