i know that building a pc need alot of things <CPU , RAM ,
Hard disks , motherboard , graphics card, Cooling and ventilation elements, and UPS> but i dont know what they do and what kind of them is good or bad, is there a website will explain it or somebody can explian it .

There are many sites out there that will walk you through building your own. Unfortunately, many, though good in their time, are sadly outdated.

Here a few suggestions/precautions:

1. Set a budget.

2. Determine the primary use for your computer. This is important, and is very much tied into #1. If you want a screaming 3D animated game machine, you will need a much bigger budget than a machine that will be used primarily for work and/or school papers, email, Internet surfing, and an occasional DVD.

3. Start with a good case and power supply. Many people over look these two critical components. The case must house AND COOL your system. A good case will provide excellent cooling, a sturdy chassis, and insulation from the fan noise. The PSU is also critical. You do not want to feed your components unstable, noisy power. Sadly many generic PSUs are thrown into cases, even good cases, just to make the sale. Do not hesitate to toss aside that PSU if the case meets your needs. Note that I would MUCH rather have a 500W Antec PSU than a 600W no-name/off-brand/generic.

4. Understand ESD. A tiny electrostatic discharge (static shocks) from your fingertips can totally destroy ESD sensitive devices, such as RAM, ICs, CPU, etc. yet be so tiny that you are not even aware that a discharge occurred! I recommend the use of an anti-static wristband for newbies and pros alike.

5. The "sweet-spot" for RAM is often considered 1Gb. I used a modified version of that rule and say 1Gb per core. So, if you select a dual core processor, I recommend getting 2 Gb. And since nearly all new motherboards support "dual-channel" RAM, make sure you get 2 X 1Gb RAM modules. Most makers sell matched pairs intended for dual-channel applications.

I applaud you for including an UPS in your list. I have been recommending EVERYONE use an UPS for over 10 years. If you live in an apartment, you need an UPS. If you have a toaster, microwave, hair dryer, refrigerator, oven, clothes iron or another high wattage appliance in your home, you need an UPS, a good UPS with AVR - automatic voltage regulation. It is important to note that battery backup is only the icing on the cake, and not the primary advantage of an UPS.

If you use a CRT monitor, you will need a bigger UPS, or ensure the monitor is not plugged into the battery side. If you use 1 or 2 LCDs, then a 1000VA UPS will easily support both monitors, your PC, AND all your networking equipment (router, modem, WAP).

Here are a couple sites I found that seem pretty current.

http://computer.howstuffworks.com/build-a-computer.htm

http://www.techpowerup.com/articles/other/144


One of the harder things builders have to ensure is that the motherboard they choose supports the CPU they want to use, and the RAM they buy. This is not easy, given the many options out there. Therefore I recommend you check out MWave's "Motherboard Bundles" Wizard. This is a great tool because you can start with the motherboard of your choice, (or CPU of your choice), and the Wizard will provide a list of boards (or CPUs) and RAM that are compatible with your choice. They've done the homework for you.

And especially nice for first time builders, for only $9 more, they will mount the CPU and HSF, install the RAM, and test it all for you. This great as not only did the Wizard ensure your parts are compatible, but the testing ensures your specific parts work, and work together - not always a sure thing. A good warm fuzzy for only $9.

Of course you don't have to buy there and can just use their Wizard to research parts, but I have found their prices to be competitive with my other favorite sites, NewEgg, and ZipZoomFly.

i want to know how to determine what those thing does like for example i find this cpu in ebay: the cpu have: INTEL PENTIUM III PROCESSOR / CPU
1.40GHz / 512K / 400MHz and


Manufacturer
Intel

Manufacturer Part Number
SL5XL (sSpec Number)

Processor Type
PENTIUM III Processor
Clock Speed
1.40GHz
Package Type
370 Pin
Bus Speed
133 MHz
Core Stepping
TA1
Cache Memory
512K
CPU ID
06B1

Quantity
1 Processor


how would i know if the cpu is good or bad so i need someone to teach me those thing like what those thing mean.

Plugging into Google and read is the best way to learn - besides taking a couple courses at your local community college.

Tom's Hardware is also a good source.

Do note that a Pentium III is ancient technology - so you don't want to go there for a new PC.

you dont know what they mean ? the only thing i know about the thing on top about cpu is the ID

Great post by Digerati.

The only thing I add is, if you can help it, do NOT buy electronics through e-bay (unless it is an established business that sells thru e-bay). I know of several people who have gotten burned very badly buying ELECTRONICS thru e-bay.

Good luck

the ebay thing is only a example .

Originally Posted by zerozone

you dont know what they mean ? the only thing i know about the thing on top about cpu is the ID

Yes, I know what they mean (except TA1 or 06B1) - but it would take pages of typing to explain but still would not do you much good because as I said, you are asking about ancient technology with the PIII. The P4 has been out for many years and has gone through many evolutionary changes, as have AMD CPUs.

If you are interested in learning about PCs, then you need to do your own homework and the Tom's site I mentioned is a great place to do that. Then for sure, ask specific questions for those things you don't understand.

Please understand that no disrespect is meant here - you are just asking for too much information that would require extensive time to explain (1) and (2) there are several site's out there dedicated to that.

Using MWave's Motherboard Wizard to configure motherboard/CPU/RAM combinations will help you to understand some of the differences in available products, including some of the information you seek, such as CPU type, sockets, bus speeds, cache, etc.

BTW - the CPU ID is not important.

Perhaps if you told us what you are trying to do, we can better assist you.

@joeofeg - Thanks and I agree - you take your chances on eBay. I use the sites mentioned above for most of my purchases - I like being able to call their customer support and talk to someone who can actually do something about the product I am having problems with. Getting an RMA through eBay is not likely to happen.

i want to learn thing about pc, can you give me some site.
i dont have homeworks about pc

I already told you about Toms Hardware, c|net is also popular.