First Check it the Wireless is turned on in the modem.
You must see the wireless light glow on.
If the WIFI is not turned ON, Check this link to Enable WIFI : How to Enable WIFI.
Before configuring wireless, connect your laptop through ethernet and connect it to http://192.168.1.1
If you were asked for username and password, give the username and password of your modem.
by default BSNL modems have username : admin and password : admin
After login, you will get the router configuration. Here, click on the Wireless Tab.
In Wireless section, give some name in the SSID (Serivce Set Identifiers), this SSID is also know as wireless network name.
Then click on the Security tab below the Wireless Tab. The name given for SSID will appear here.
Select WPA-PSK in Network Authentication and give the WPA Pre-Shared Key.
This Key is the Password for Secured wireless network,Which we need to give in the laptop to authenticate and connect to the secured network.
Give 0 (Zero) for WPA Group Rekey Interval.
After completing the above, Click SAVE/APPLY button. Your wirless configuration is saved now.
Now Reboot your modem, Go to Management tab, and click Save/Reboot
Wait till your modem restarts, Now your wirless network is ready for use.
Connecting to Wireless Network after configuring the WIFI.
Connect your laptop to the wireless network and you will be asked for the password. This is the one which you gave for WPA Pre-Shared Key.
Once you give the password correctly, you will be connected to the Secured Wireless network