To install a power supply, first make sure it is the right wattage for the board. Too high and it will short out the motherboard, too low and peripherals will not work properly. Align the power supply along the back of the case and secure in place with screws. Take the cables, and locate the power supply slots on the mother board. They should only fit one way. Insert the power cable into the slots. Close the case, power on the computer and the fan should begin to run.