If you want to connect this device directly to your Internet service provider's connection, you must have it provisioned by them, which most do not do. The best thing to do is to call and ask. Mine had initially confirmed provisioning, but then didn't do it, which is why I sent the device back. You can also connect the router behind your ISP's router, forward all the necessary ports and set up a double NAT. A few access points, which are best connected to your router by cable via a switch, are also sufficient purely for the WLAN. For MESH, however, you first need a MESH-capable device on the router (e.g. the double NAT solution) and then MESH-capable access points. But I have no experience with this. Double NAT works for me and is not noticeable in everyday life. Router ISP -> Firewall -> Switch -> Access points

To extend a WLAN, a wireless extender would actually be the right thing. I personally have the Zyxel WX3100-T0 and have connected it with a LAN cable. But it also works without a LAN cable. I was only able to set it up via the app and not directly via the router/extender interface.
Zyxel WX3100 WLAN-Mesh-Repeater