How to Add a Password to Your Wireless Internet (WiFi)

You should connect your computer to your router via an ethernet cable in an open port.  After that you can access your routers settings by going to your "Home" IP address. In your Internet browser of choice, type in 192.168.1.1 (or 192.168.0.1) in the URL or address bar. This should bring up a login and password prompt window. The default password for most routers is "admin" and you should type that into both fields. If this doesn't work, try leaving on field blank and typing admin into the other. If that fails, consult any available support for your specific router manufacturer.

click on "Wireless" >> >  "Security" 

select WPA2-PSK in Network Authentication 

and add password of your choice in WPA Pre-Shared Key option .

if you forget the configuration you could try resetting your modem/router by pressing the pinhole reset button on the device .