If you have multiple computer systems at home, there are several advantages to networking them together, some of which include:

Printer Sharing
Share a common printer with all of computers at home.

File Sharing
Share files from computer to computer without having to copy them to a diskette or CD.

Sharing an internet connection
Share your DSL or Cable Modem with all the computers in the house.

What will this require?

A network card for each computer

Most new computers come with network cards in them. If you have an older computer with no card, then an ethernet card will have to be purchased for that computer. If you desire a wireless network, then wireless network cards will have to be purchased for each computer.

Ethernet connections at each computer

Wireless Network: If you are running a wireless network, your wireless ethernet card will provide your connection to your home network. No further connection is needed.

Cabled: You will need to run an ethernet cable to each computer location within the house. This is different than the phone cabling. A connector or an ethernet jack will be installed where each cable ends.

Ethernet Router

This is the hub that connects all of your computers together and creates the network. This will be a regular or wireless hub depending on what kind of network you are installing.