No worries. You siply take your PSU, get the large 20 (sopmetimes 24) pin power plug that would connect to the motherboard, and roughly in the middle there will be a green ground wire. You simply take the paper clip and push one end into the metal pin hole thing on the power plug, and then bend the other end into one of the black wires copper connectors. Duck tape the sucker down and the moment you plug your PSU into the wall it will power up. You can buy fancy tools to do it (psu testers and such) but at the end of the day a paperclip is all you need.
So from that picture, you would simply short PS-ON and COM located directly beneath it (or any pin/wire labeled as COM). That is how a computer works, when it's plugged in, the pressing of the power button causes the PS_ON to be shorted and as such power the PSU up. It's a bit more dependable and depending on the PSU you buy you can be sure it's not gonna melt anything or fail etc.