COMPUTER PARTS!!!

Modem - changes the information from binary to audible and availiable for people. Allows you to connect to the internet.
PCI slots - located on the motherboard, allow you to plug in your devices - through appropriate cards. Make sure though that your slot is up-to-date with your card or else it won't fit. If it does not fit, then leave it alone, don't hammer it in.
Video Card - controls the picture on your screen. Some video cards come built-in your motherboard. They are usually not the best quality, but you can live with it. However, if you play a lot of video games, then you might want to buy a more advanced video card, so that all the images and pictures and parts of the game run smoothly. Same goes if you are working with images (e.g. using Photoshop a lot like I do.)
Audio Card - that's right, it controls what you can hear, all the sounds. It is pretty similar to a video card when it comes to quality and upgrading to a better card. If you are the type of listener, who cares about every single note in a song, then perhaps it's a good idea to buy a more advanced card. If you are using your computer just to fo homework and chat on MSN, then you probably can go with the video and audio cards you have built-in your motherboard (if there are ones built-in.)

By Ardavan.Z