First, turn off the router and the DSL modem. Connect the Ethernet cable from the DSL modem to the WAN port on the router. You can connect up to three other devices (computers, printers, etc.) that have Ethernet to the router's other LAN ports. Turn on the DSL modem first. Wait for the status lights to show it is communicating with your ISP. Then turn on the router. Wait for the amber light to start blinking.
Open Airport Utility in the Utilities folder in order to configure the router. You will need to setup your wireless network with a name. You will need to configure wireless security to WPA2/WPA2 Personal and a password.The latter will be needed for others to connect to your wireless network.