Make sure that your Belong 4353 is plugged into a power outlet and switched on.
FTTC, FTTP, and HFC connections: run an ethernet cable from the red WAN port to the correct port on your NBN connection box:
FTTP: the UNI-D port as described in your onboarding email.
FTTC: the 'GATEWAY' port.
HFC: the 'UNI-D1' port.
FTTN and FTTB connections: run a phone cable from the grey DSL port on the Belong modem to a phone port in the wall.
Put a pin or toothpick in the small 'RESET' hole in the back of the Belong for 10 seconds. Wait for the Belong to reset. This can take a few minutes. Connect to the Belong's Wi-Fi network. The Wi-Fi name and password will be on the sticker on its base. Check for an internet connection.