When I first decided I wanted to build a computer I did a ton of research and made sure that I understood all the basics. I wanted to know what exactly I needed to make this process easier. I knew I wanted a gaming PC, that was my first decision. Then I looked online and found out what a CPU was, and RAM, and all the components of a computer. It really wasn't as bad or hard to understand as I thought it would be. Now you are taking that same path and want to build a computer of your very own. It isn't hard at all, you just have to understand what each part does and how they work together. To begin I have listed all the parts and what they are / do. Then I will explain how to put them all together in another thread.
Central Processing Unit
The central processing unit or CPU or processor is the head honcho, the brains of the whole operation. It performs all the instructions for all the software that you run. How your games perform is directly related to the CPU. There are three types of processor: 2 core, 3 core, and 4 core. 2 core is good for casual gaming and basic home / office use. 3 core is made for gaming some multitasking. 4 core is good for gaming but especially multitasking (running more than one program at once).
There are two companies that make CPUs. I'm sure you've heard of Intel processors. As of right now they are leading the way in high performance gaming processors with their i3, i5, and i7 series CPUs. Really expensive though, but they do make other processors that would still be very good for your first gaming build. Ones like the Core 2 Duo or Core 2 Quad are very nice processors. Still on the expensive side but well worth it if you have the money.
On the other side, Intel's rival, competitor, and my personal favorite, AMD processors. AMD makes amazing processors and are much more affordable than Intel. Intel makes a processor based on high quality and high performance, AMD focuses on quality, performance, and affordability. AMD makes 2 core, 3 core, and 4 core processors. For gaming the best they offer is the Phenom II X3 which is a 3 core processor. You can get a Phenom II X4 but your games will better benefit from a 3 core. If you're on a budget then AMD is there for your gaming needs with the Anthlon II X2, X3, and X4 processors. So no matter which company you choose for your first build, you will be satisfied.
This component is a big PCB (printed circuit board) that holds most of your internal parts. It basically relays all the information between the internal components. The processor goes here, your RAM, and your video card plug directly into the mobo (short for motherboard). Your hard drive, optical drive, and power supply plug into it via cable. Basically the mobo is pretty simple to pick out, you just need to find out what it supports. It's not a one size fits all type of deal so do your research and make sure your other parts match what the mobo supports or else you won't have a computer. Motherboards come in different perimeter sizes, the most common being micro ATX and ATX. Those two are really the only types you will use, the cases you will be shopping for will support both. A lot of different companies make motherboards but the most popular seem to be GIGABYTE, ASUS, MSI, and EVGA. You will get a great board if you select one of these.
Random Access Memory
The random access memory or RAM is responsible for storing running programs so the more memory you have, the faster your games will run. There are different types of RAM out there but it's really simple to choose. The most common and most popular RAM you will see and use is DDR SDRAM. DDR (double data rate) SDRAM (synchronous dynamic random access memory) is basically the norm today and has evolved from the past. So far there has been DDR SDRAM, DDR2 SDRAM, and now the fastest, DDR3 SDRAM. For a gaming build you definitely want DDR3 so find a motherboard that supports DDR3. *NOTE*:The RAM slots on a motherboard are different for each type of RAM, so DDR will not fit into a DDR2 slot and DDR2 will not fit into a DDR3 slot. DO YOUR RESEARCH! You also need to know how much RAM to get. Most motherboards can support up to 12-16GB of RAM but you won't need that much. Most gamers use 2-4GB, I recommend 4GB. Also buy the RAM in pairs, so 4GB is actually two sticks with 2GB on each. That would be a lot smoother and beneficial than one stick of 4GB. Good companies to look for: CORSAIR, G.SKILL, Kingston, OCZ, Patriot, and Crucial.
The Graphics Card
This component is vital to any gaming system. If you want a good gaming system you need a better than good graphics card. Just like the CPU world, the graphics world has only two companies making the world's best graphic chipsets available: ATI and nVidia. Competition is fierce between these two, but as of now ATI just released their newest chipset making it the fastest graphics card on the planet. Now, the way to tell these two apart is by model name. ATI is responsible for the Radeon series cards and nVidia is responsible for the GeForce series. Unlike Intel and AMD both ATI and nVidia licence their chipsets to other companies who build the cards using the chipsets. Graphics cards connect to the motherboard via what's called a PCI Express interface. PCI (Peripheral Component Interconnect) Express is the best and can be found on all the latest motherboards. The updated interface is now PCI Express 2.0 which is what the all the current cards are using. The form is x16 so be sure to look for that when selecting a video card. Now, for gaming you need a great video card so make your choice between ATI or nVidia. On the ATI side, you will want the Radeon series. There is many models to chose from so choose one of the following: ATI Radeon HD 4770, 4850, 4890, 5770, or the 5850. They do go higher but those are really expensive and really advanced. On the nVidia side I would recommend the GeForce GTX 200 series, the GeForce GTS 200 series, or the GeForce 9 series cards. Either way, your graphics experience will be amazing.
These are the main components that you will shop for and the ones you need to know most about. Just remember to make sure that everything is compatible with each other and that the motherboard supports your other choices. Good luck and if you have any questions or want to know about the other components please ask and / or reply here.