The article is based on the condition that you already have a router and only want TP-LINK router to extend the wireless network range via a LAN cable. We don’t need WAN port on the TP-LINK router in this network.
Connect your computer to anther LAN port through Ethernet cable, then login to TP-LINK web interface through the IP address on the bottom label by the following tips:
Go to Network ->LAN on the left side menu,change the LAN IP address of TP-LINK router to the same segment of the main router.( For example, if your main router gets the IP address of 192.168.2.1, 192.168.2.X (1<X<254) is recommended for TP-LINK router.)
After that, it would require a Reboot. Please click OK to reboot and then relogin to TP-LINK page with the new IP address
Configure the wireless
Go to Wireless->Wireless Settings page, configure the SSID (Network name) and Channel. (If it is a dual band device, please don’t forget to select the Band.) Click Save button.
Go to Wireless->Wireless Security page, configure the wireless security. Here WPA-PSK/AES is recommended. PSK Password is the key of your wireless.
Go to DHCP on the left side menu, disable the DHCP Server and click Save button.
Go to System Tools->Reboot page, click Reboot button to reboot the device.
Connect the main router to the LAN port on TP-Link router through Ethernet cable.