First, you need to determine your price range and what purpose you want to use your computer for. If you only want to use word processing software and work on the internet, then you may not need to spend too much money. At the same time, if you are looking to make a computer for playing the latest games, then you will have to buy more parts and spend a fair amount of cash.
Purchase a motherboard and a casing for your computer. Fit the motherboard into the casing. Here, you should make sure that the motherboard that you purchase has all the slots available for the components that you want to install in your computer. Use the screws to mount the motherboard into the casing.
Now take a processor and attach it to the motherboard. You should purchase a processor that complements the motherboard. For instance, you cannot use an Intel i3 processor on a board that has the capability of supporting an Intel Core2Duo processor. After installing the processor, do not forget to install a heat sink / cooling fan right on top of it.
It is now time to install RAM sticks into your computer. Here, you should install RAM according to the operating system you plan to install on your computer. For example, if you are planning to use Windows XP on your computer, then 1GB RAM will be more than enough. On the other hand, you will need at least 2 GB RAM if you want to install and use Windows 7 or Windows 8. Also, you can install RAM as per the requirements of the software and games you plan to install in your computer.
Usually, the latest motherboards come with audio, video and Ethernet cards. If, for any reason, you do not have them installed in your motherboard, or you want to upgrade them using your own, then you can install them on their respective slots. You can check for the appropriate slots after reading the user manual that come with the cards.
Now you need to attach a hard drive with your computer. You can either choose IDE or SATA, depending on the slots available on your motherboard. If you have both options available, then you should go with SATA drives, as they are faster compared to IDE. Also, you should attach the DVD drive or any other disk drive that you want.
Mount the power supply to the inside top of your casing. You will have a number of power cables coming out of the power supply. Attach the main cable with the motherboard and others with the devices such as hard drive and DVD drives.
Once you are done with adding all the components, insert CD or DVD for the operating system that you want to use and complete the installation process.