As complex as it may sound, building a PC is actually quite simple; that is, if you know what you are doing. There are several steps involved and it usually takes a couple of hours to actually put the parts together. The best place for computer parts is www.newegg.com.
Please note! All monentary values are given in US dollars (USD).
Before we get started, here is a little word of warning that can save your computer: make sure that there is no static electricity on you when you touch the electric-sensitive components of your computer. You can do this (grounding yourself) by touching something metal touching the ground or by plugging in your PSU(provided it as a metal outside) and touch that. Alternatively, you can find an anti-static wristband. Not grounding yourself can potentially short one of the components, which are quite expensive and a pain to replace.
1. First, it is important to establish what the computer will be used for and how much you are willing to spend on it. For example, a serious gamer might want to invest $1200 in a high end computer with a $500 graphics card. On the other hand, a casual user that is only going to use the computer for general web browsing, multimedia, and/or some casual gaming, can look for one in the $500-$800 range.
2. Next comes picking out the parts. In general, a good motherboard ($100+) and a good power supply ($40+) are recommended. The motherboard is the core of the system and cannot be replaced without the purchase of another copy of the operating system. Important aspects to look for in motherboards are PCI Express slots, plenty of USB ports (USB 2.0 is currently mainstream), at least 4 RAM slots with a minimum total capacity of 16 gigabytes, a current CPU socket compatible with processor you are buying, plenty of SATA ports, and the correct form factor (Mini-ATX for extremely compact cases, Micro-ATX for mid tower cases, and ATX for mid or full tower cases). In power supplies, it is important to look for a good wattage (400+) in order to have good upgrade potential as GPUs and CPUs tend to be power hungry. Earthwatts power supplies have some of the best customer satisfaction. Also, it is important to look for power supplies that are bronze silver or gold rated. Another important component is the drive. There are two main drives nowadays: hard drives and solid state drives, the latter of which is substantially more expensive. Hard drives are very common and generally range from $50-$150 for a decent hard drive. When choosing hard drives it is very important to keep in mind the intended use of the drive. While 500 gigabytes may be adequate for the average user, it is definitely not enough for years of 8+ megapixel photos and full HD video (1080p). For those purposes a hard drive of at least a terabyte (1000 gigabytes) is required. There are two main speeds of hard drives 5400 revolutions per minute (RPM) and 7200 RPM; the 7200 RPM hard drives are significantly faster and I recommend them for any desktop user. Finally, there is hard drive cache which should be at least 16 megabytes because as with all cache, the more the merrier.It is important that the hard drive connects with a SATA cable. Solid state drives are faster and more reliable versions of hard drives as they contain very few moving parts. The downside is that they are very expensive; I recommend sticking to hard drives unless you have $200-$500 to spare. In addition, there is also the vital component known as RAM. Essentially, it speeds everything up and similarly to cache; the more the merrier. It is recommended to have at least 4 gigabytes of RAM and preferably 8. There are multiple frequencies of RAM; it is vital to choose one that is compatible with the motherboard. DDR3 RAM is the most frequently used one and consists of an immense range of frequencies with higher frequencies meaning faster RAM. However, the higher frequencies only come in handy during gaming or other high performance computing. Remember that is always best not to mix and match RAM. The computer case should correspond to the motherboard size and the quantity and size of graphics cards. Computer cases are truly a matter of personal preference. Similarly, there are a wide range of viable DVD/Blue Ray drives available; the drive should also connect with a SATA cable. The last two components are the GPU and CPU. The majority of CPUs are produced by AMD and Intel. AMD processors tend to have a higher performance to cost ratio, thus making them preferred by many PC builders. Intel, on the other hand, have slightly better performing processors for a significantly increased price. While looking for processors, one has to keep in mind cache. L1 is the fastest, but most processors of the same core count have the same amount of it. L2 is next and most of the same core count have the same amount, with the notable exception of Intel Core 2 Quad which has 12 megabytes and the AMD Zambezi processors, as opposed to the 2 megabytes in most quad cores. Finally there is L3 cache which is usually around 6 megabytes for quads and dual cores and 8 megabytes in eight cores. For the average user a 2-4 core is recommended; for gaming a 4-8 core is preferable. In general, the more cache and cores the better. Finally, there are GPUs. A discrete GPU is favored by many (separate from the one built into the motherboard or cpu) and most mid-end GPUs cost under $100. The two main companies that manufacture GPUs are NVIDIA and AMD. NVIDIA goes hand in hand with Intel CPUs, while AMD goes hand in hand with AMD CPUs. However, they work well together either way. When shopping for GPUs it is critical to look for at least 512 megabytes of memory (preferably 1 gigabyte), a core clock of at least 500 MHz, and GDDR5 memory. Also, be sure to buy a graphics card that matched the PCI slots of the motherboard and size of the case. Gamers may want to invest in a higher end video card.
3. One of the most important aspects in building a PC is choosing an operating system (OS). There are two main operating systems for computer builders; Linux and Windows. Linux is a free operating system with not nearly as many applications as Windows. There are multiple releases of Linux, but Ubuntu is the preferred one. Windows also multiple releases with the most recent one being Windows 7. Windows 7 comes in three main versions: Home Premium, Professional, and Ultimate. Home Premium is for the casual home computer user, while the other two have more features for anyone who can take advantage of them. For more information, go to http://www.sevenforums.com/tutorials/14422-compare-windows-7-editions.html.
4. Next, comes the putting together of the computer itself. Before doing so, one has to decide if the computer has enough ventilation. Without proper ventilation, the components will not last nearly as long as long as they could have with proper ventilation. That is due to the immense amounts of heat that the CPU and GPU generate. The average PC requires at least two cooling fans: one for the CPU and one on the rear vent of the case. The rear fan should be forcing air out the back of the case, while the CPU fan should be blowing air into the CPU heatsink.