computer fans... how the hell??

ok, so im dividing my grow box up into a few sections (due to some security issues im having to get rid of a couple boxes and shrink my shit down). my boxes are small to begin with, each of them are 36" x 22" x 24". i had been using separate boxes for different stages of grow.
ive been using desk lamps to keep it cool, but theyre too big to use once i divide the box im keeping. so im trying to figure out how to use computer fans.
im not that good with wiring, so i cant figure out how to make one work in a box. they have this computer wire thing so that you can connect them to a computer, so how do i connect it to something else, so i can plug it into the wall??
im really confused.

thanks

** I forgot to include that I need 3 fans all wired to the same adaptor. i found info on wiring 2 fans, but i'm not sure if wiring 3 would cause a short or other electrical problem that could kill my plants... or me

I typed a long response... then I noticed this thread which describes it better than I ever could:

https://www.rollitup.org/do-yourself/4105-computer-fan-wiring.html

Knock yourself out.

If you have a spare PSU use that by jumping the only green wire to any black wire in the 20-pin Motherboard clip. At that point just start plugging in fans : )

i tried searching for posts about it and couldn't find any. so thanks!

Today is your lucky day I guess . Here are some pictures of what I mean though. Notice I have the little red wire in the pin were the green wire leads. I then plug the little red wire into any pin with a black wire.