how do i connect fans to a power supply

I have an old pc and i want to use the fans in my grow box. Problem is I have no idea how to connect the fans to the power supply. How does one do that?

You have to make the power supply think you pushed the power button attached to a motherboard on it, so it depends on the power supply as to what you need to cross to make that happen. There are standard ATX power supplies with standard pinouts, but there are some oddball ones out there like Dell uses a different pinout, so I don't want to send you down the wrong path to get this working

I did it for my Server Case CFL grow.

If you have an old phone charger you can wire it to that.