The AirPort Extreme router takes the signal from your cable modem and distributes it over a wireless area network so multiple devices can connect to the Internet. Use an Ethernet cable to make the connection between the modem and the AirPort router. Once the connection is made, the Airport Extreme will immediately begin sending out a signal to your Wi-Fi enabled devices. Writer Bio

How to Connect an AirPort Extreme to a Cable Modem - 53