OK, the brains of the computer is the processor. The processor processes or sorts information like your own brain does.
The processor sits on top of the motherbaord and communicates to the rest of the computer and the user, (you).
The proceessor can be a single prossessor a dual (or double) processor or even a quad processor! Dual and quad are best. Intel or AMD? Some use one or the other or both. I've used both but tend to prefer AMD. Although the Intel quad processor has my interest too! Great for gaming!
The keyboard and mouse are Human interface devices, (HID) and let you tell the computer what you want and want it to do.
The monitor is for you to see what the computer is doing, like a translator for pictures, words, and video or graphics; (video games). A flat panel monitor means that it is thin (like about and inch or two thick).
Between the monitor and the computer is a video card which should have memory on it. 256 MB, (Mega Bytes or millions bits of information) is now standard.
A byte is a 7 letter "word" with an 8th letter of either "0" or "1" at the end of it. 0 tells it to turn off a transistor after doing the task and 1 tells it to turn on the transistor. (Never mind but it is nice to know and to understand).
So, often the case and power supply, (PS), include the motherboard and processor already and may include an additional video card.
It could have "on board video" if it is a less expensive system. But I suggest getting a system with a video card that has its own memory and does not borrow from the computer itself or will slow it down.
Basically you have to ask yourself what you want the computer to do. Is it for school? To play games on? Do you need it portable or will you be using it at home only; (Called a desktop computer). A laptop is portable.
The cheapest upgrade that you can add to improve a computer is memory and make it faster. There are many types of memory : DDR2 is probably the more current memory to date. It's just a name to classify the type of memory. There are different types for desk tops and laptops.
Hard drives are multiple disk drives, (like a stack of re-writeable cd's but better and faster!) that store files, music, pictures, information, and video or games on. A Serial ATA drive or SATA is faster and
more reliable than a standard 100/133 IDE drive. IDE drives are ok but SATA rocks!
By the way the higher the hard drive space, (250 GB on up to 1TB) GigaByte billion bits of info and Terabyte or trillion bits of information; The higher the Hard drive specs the more expensive and more that it can store.
Let's see, Processor, motherboard, keyboard & mouse, monitor & video (vid) card, memory and hard drive(s).
Yup that should help you to get started. A basic system should cost between $475.00-$675.00, whereas a nicer system should cost even more, like $800.00 - $1200.00.
Oh I almost forgot, the operating sytem! This tells the computer what it is supposed to do on start-up. (Get out of bed, brush your teeth and comb your hair) as an example.
Currently Microsoft is pushing it's newest software the Vista operating system. I have heard good and bad about it. I understand it just takes some getting use to and is suppose to be intuitive to your wants and needs.
Good luck hope this helps!