I do not really understand your question, but the important parts in building just the computer are, a Processor, Graphics Card, Power Supply, Motherboard, Hard drive and/or/both Solid state drive, RAM, and a Case. Some things that can, and will be helpful in a PC Build, are, Case Fans, After Market CPU Fan (If you are overclocking that is), Optical Drive, and a Card Reader. Some peripherals are, Monitor, Keyboard, Mouse, Speakers, and a headset. Now this is all for a gaming PC. For a regular desktop for say like a home office, all you need is the PC parts of course, a monitor, keyboard and mouse and perhaps speakers. What kind of PC are you looking in to building? And if I may ask what kind of budget? If that is you are building a computer and you are asking because you do not know what you need in a computer of course.