This document provides a 3-step configuration guide for the MTNL FTTH ONT 100C device: 1) Access the device admin page at http://192.168.1.1/ with username "root" and password "system", 2) Configure the WAN settings including username as the telephone number suffixed with "@a" and password as the CA number, and 3) Reboot the device by clicking "Reboot" under "Maintain" to complete the configuration.