First off, great thread. This could indeed be very helpful.
Second, peripherals are simply external devices one attaches and/or connects to a PC (or even a console) to enable specific functions. A keyboard or a mouse are peripherals, a controller is a peripheral. A display, like a TV, monitor or whatever is a peripheral. The remote for your TV or cable box is a peripheral.
When it comes to building PC's, some more specific advice is required. I'd do what I can for people, but to go though everything I know it would be inconveniently long for all off us. So, I'll offer instead a Q/A style thing on this thread. And not just me, I'm sure others will try thier best to help.. Ask, and I'm sure the community will do our best to answer.
The only stupid question is one that's never asked.