I used to laugh at people who got panicky when they needed to set up their own PCs. They'd worry what would go wrong if they plugged something in the wrong way.
I'd reassure them that it was really easy. The cables only connect one way. You can tell by the plugs and jacks how they fit together. You just have to match up the shapes of the plugs to the shapes of the jacks. Of course you needed to figure out how all the audio cables work; the microphone and the speakers are sometimes colour coded. If not, you pay attention to which peripheral the cable is coming from and you look for the little icon on the back of the CPU and choose the correct one. And the webcam and the printer are best to hook in while you're down on the floor with a flashlight looking for the correct jack. The mouse too. Match up cables and their plugs to the jacks in your CPU and you'll be all set.
You should end up with something like the photo shown here. A bunch of different cables heading down through a hole in your desk to the CPU beneath. The last step is to hook your modem or network cable up from the CPU.
Yesterday I unpacked my new iMac. Here's the sum total of the cable connections required to set the thing up: one AC power cord heading to the wall. End of story.