You probably already have a computer at home, and since you want to buy a new one, the one you have is now 3-5 years old. Not much in human years, but a computer year is closer to dog years. Even if you want a new computer, you probably have a lot of files, photos, music, etc. on your old computer that you want to transfer to your new one. This is actually the first step in buying a new computer; Make a backup copy of all the files you want to save and do not format your old computer until you are 100% sure that you have copied all the files you want.
The big question when buying a new computer is simply which one. There are literally 100s of different models to choose from. They all have confusing names and parts like geforce, asus, x86, 64bit and so on. If you want to คอมพิวเตอร์รุ่นใหม่ that you can use to go online, check emails and maybe use office, there is no need to understand any of the model names. Most likely, any computer in the $ 600-1000 price range will do more than fine. Just make sure the computer you buy comes with Windows7 and Office for windows as this costs extra if they are not.
For those who want to buy not only a workstation but also an entire entertainment package, you need a little more technical info and should expect a somewhat higher price range. A decent gaming computer is priced from around $ 1000, the sky is the limit. You want a multi-threaded cpu, a good graphics card and at least 4 GB of RAM. If this sounds like Greek to you, visit a computer store and ask questions, a lot of questions. Make sure the computer you buy fits every need. Make sure everything you need is included in the price. Decide not to buy the first time you are in the store, get the specifications for the computer they suggest, go online and search for a computer forum and ask them if they agree that this is a good setup.