By default, RUT bridges the wired LAN and WiFi under one interface called br-lan. This means when you're connected to the RUT via WiFi, you should have access to devices on the ethernet LAN ports as well. The router's LAN ports come with a pre-configured DHCP server, allowing LAN devices to automatically acquire IP addresses when they connect to the RUT. As a result, you can easily reach these devices over WiFi.
If you find it necessary to assign specific, static IP addresses to the connected devices, there is an option to set static IP leases in Network -> Interfaces -> Static leases.
The WiFi password can also be changed through the router's WiFi security settings, where you can configure other security settings as well. For this, simply navigate to Network -> Wireless -> edit WiFi instance -> Security.
More information about the WiFi is available on our wiki page here (RUTX11 page, but is similar to other devices as well).