Hello Binoj,
a starting point can be the following
http://www.cisco.com/en/US/docs/routers/access/800/850/hardware/quick/guide/857qseng.html#wp1031163
the first step is to get a working console connection to the router because it can have multiple interfaces but no ip address is on them.
If the router is new a New Router configuration setup is presented that allows to setup some basic parameters like an ip address in the LAN interface, hostname, login password, enable password.
You can choice to skip this menu and performs all config using CLI commands
Hope to help
Giuseppe
