First of all, when you insert SIM card into your router, make sure you can connect to your operator. If everything is working you will be able to see something like this in WebUI status page:
If you SIM fails to connect to the network, make sure your APN settings are correct. Navigate Network > Interfaces > Your mobile interface and uncheck Auto APN slider, put custom APN phrase that your operator provides.
When you successfully establish mobile connection to the internet, all devices connected to the router ethernet ports should acquire IP address from your router and connect to the internet if all other configuration is left unchanged.
To connect your devices to router network via WiFi, navigate Network > Wireless and configure Wireless AP interface by pressing Add button.
If you will have any further questions, do not hesitate to ask.