These are the plugs and sockets on the back on your computer. Once upon a time, the main ports were Serial and Parallel which were used to connect printers and scanners but they have been overtaken in the main by USB. This can be used to connect almost anything to your PC including printers, scanners, a mouse, external hard drives, cameras, music interfaces, modems, routers and so on.

The current slot for plugging in expansion cards is the PCI-E (PCI Express) which is replacing the PCI connector.

Another popular port is FireWire which tends to be used for more demanding applications like digital audio and video cameras but this seems to be slowly losing ground to USB, too.

You'll usually find Ethernet connections round the back, for connecting computers together to create a LAN (Local Area Network).

Other ports you may see are PS2 for connecting a keyboard and mouse.

Port connections are usually built into the motherboard although you can often add additional ports such as USB and FireWire by plugging in an expansion card. Most computers have at least four USB ports. If you want to add a lot of peripheral equipment, it's important that your machine has enough connections although if you're short of USB ports, for example, you can add a USB hub to get more.