My question is how can I make the fans in my computer keep running for a period after it shuts off to cool it down/for looks. I've seen it done in computer shops where it is just the powersupply and the fans. I was just wondering cause it wanted to do that and if I could also control the fan running after the power is off by a switch or etc

Thank you to anyone who can answer my question thanks again

Put them on separate power sources that are not directly tied to the on/off button.

I am kind of confused would you mind going into detail a little bit to as how you would do it?