There is a bundle of cables that come in from the top front (fan control, USB, audio, power, reset, HDD/SSD activity light). There are three connectors on that bundle that fit the connectors on the two front fans and the side fan (they only fit one way and they're the only thing the fans can plug into.
Then, you plug the four-pin molex from that bundle into a molex from your power supply. That's how you power the fans and control the speed with the 3-position switch.