What port on the TP-Link router you've connected the 8 port switch to? You should just use its LAN port to avoid double NATting.
To configure it as an AP/switch only, set its LAN IP to 192.168.0.50(or other number), subnet mask to 255.255.255.0 (assuming it's the same as your modem/router). set its WAN IP to a different IP as 192.168.0.0/24, and disable its DHCP service. You can then just use its LAN ports for other wired devices and don't connect anything on its WAN port.
Those settings assume you don't require the TP-Link to use a different network.