IT guy here.
Simple, black=negative
Red=Positive 12v
If you wire them backwards, they'll just turn backwards. Normally the white wire is the rpm sensor, it's used to send the rpm of the fan to the computer to insure the fan is working properly. DISREGARD THAT WIRE
The 4th wire is the low voltage, 5v I beleive, to make the fan run silent.
DISREGARD THAT WIRE
Little tip for those who wants to install computer fans. Under a 12v power supply, they can be quite noisy, "high pitch noise". You should run them at 5v (they will simply run slower thus quieter(use the same red wire as the 12v)). What 5v power supply that everyone has a crap load of?
USB phone chargers!! If you run multiple fans off the same power supply, just make sure that the total amps from the fans don't exceed the amp output of the usb charger.
That's it dirt cheap fans. Free Power supply.