If you have multiple computers in your home or office and want to share files, printers, scanners or net storage devices, then perhaps you're in the market for a network. With a network you can share a high-speed internet connection, play games against others on the network, and so forth.
Wired or wireless? That depends...
Wired Networks
Wired networks consist of multiple runs of cable from a central location (a 'Head-End') that terminate where items to be connected are located. Most terminations are with an Ethernet/CAT5 (or better) wall plate of some type, although the cable could be run directly to the network component.
The cable type may vary somewhat, but you will usually see Category 5 as the norm.
Connections at the 'Head-End' can be made in various methods - punch down blocks, rack style patch panels or directly into switches, hubs or routers.
Most of the more recent computers come from the factory with an Ethernet connection already built in. For those that don't have a connection, costs for adapters or cards are extremely reasonable.
The benefits of wired (vs. wireless) networks include faster network speed for file transfers, etc., and overall lower cost for hardware.
Wireless Networks
Wireless networks usually consist of a wireless router (kind of a "Head- End' where your high-speed internet connection would be attached) or an Access Point (a device that connects to a hub or switch for wireless access). Many manufacturers have Routers that can be configured as an Access Point.
To connect computers, printers and other hardware to a wireless network, they must either have some type of wireless capability built in, or a wireless card or adapter for that device must be used. Wireless cards and adapters are available for laptops, desktops, PDA's, printers (wireless print servers), etc.
The benefits of wireless (vs. wired) networks include the ability to roam within the covered area; easily expandable and no cables to worry about, etc.