If you want to connect more than two Macs and hook them all up to the Internet, you need to set up an Ethernet router. You use a special Ethernet jack to connect the router to your high-speed Internet modem or to another router. Some routers also include a WiFi access point.

The exact procedure for setting up a router can vary for different models, so look over the instructions that come with it and then save them with the other papers that came with your Mac. But the installation generally goes like this:

Run an Ethernet cable from your high-speed modem to your router’s WAN port. Then run an Ethernet cable from each computer you want to wire to the network to one of the router’s LAN ports. (If you have a WiFi router, you don’t need to run a cable to a WiFi-equipped computer, though you can if you want.) You then hook up power to your router, typically by plugging the power unit that came with the router into an outlet on the wall or a power strip and then plugging the power unit’s wire into your router.

Your router has a small computer inside that knows how to send the right messages to the right computer attached to it. Most routers have blinking lights in the front that give you some clue as to what is working and active. Other types of boxes, called hubs and switches, accomplish pretty much the same thing. Routers include a number of capabilities, such as firewalls for increased security and parental controls. You configure them using your Web browser — they look like a Web site with a special address.

Devices on your Ethernet are automatically assigned IP addresses in one of the special ranges that are reserved for private networks. These never go out on the public Internet, so you and your neighbors can be using the same addresses on your home networks without a problem. These numbers are usually assigned automatically. From the outside, your local network is known by the globally unique IP address assigned to it by your Internet service provider. Your computers — you can network more than one — use their internal addresses, and your router converts those to the external address automatically as needed, a process known as Network Address Translation (NAT).