Case The aluminum (Usually) box that holds the components of the PC. These usually come with fans mounted for cooling. Care should be taken in placing the case so that airflow to the MOBO is not blocked.

USB Universal serial bus. Circuitry that provides a connection to the MOBO. Memory card readers, hard drives, floppy disk drives are examples of devices that can use USB. You can connect a maximum of 127 USB devices to a PC.

Firewire Also known as IEEE 1394. Another method of connecting to the PC. Though firewire is rated the same speed as USB2, firewire is faster because of the way Windows handles it. Typically, camcorders and Hard drives would be connected to firewire.

Modem Modulate-demodulate. Modifying a carrier signal by piggybacking a signal such as data on the carrier. When you speak on the telephone you are modulating the carrier with your voice. Internet signals are signals modulating a carrier, then demodulating the same.

There are many tutorials on building your own PC.

Read my article on "Build Your Own PC". It was a very rewarding experience for me. I cannot describe the thrill when you first turn the power on and see the Windows splash screen.