How to Use a Router as a WiFi Extender

Sometimes. The router needs a supported repeater, bridge or mesh mode for wireless use, or access point mode when connected to the main router by Ethernet. Check the exact model manual.

Only if that model provides router mode and the network connection required for it. Many extenders are designed to extend an existing network or act as wired access points, not replace a router.

A wired access point avoids using WiFi for the link back to the router and can provide a more reliable connection where you can run Ethernet. A range extender is easier where cabling is impractical, but its placement and wireless backhaul affect performance.

Only if the router models and firmware support a compatible wireless bridge, repeater or mesh configuration. Otherwise, connect the second router by Ethernet and configure it as an access point if its manual permits.