1)Open the web browser that you use: Firefox,Google Chrome,IE,or Opera and type in the IP address for your router,and press the Enter key. http://www.routeripaddress.com/< Router ip addresses can be found here
2)A window will open and then type in your routers default username and password,and press the Enter key again http://www.routerpasswords.com/< Router usernames and passwords found here
3)Navigate to the Wireless Security\Network Security Settings Tab and open it to locate or change your WEP or WPA Security Passphrase. Use WPA because it provides better security.
4)Write this Security Passphrase down and put it in a safe place to access when needed.
Did you install the router using the install cd that came with the router ?
Do you have the owners manual that came with the router ? The owners manual will have the routers address and the default user name and password to get into the routers internal settings.
Netgear uses 192.168.1.1 for the routers address which you need to type into your browsers address bar to open the log in window.
Once you type in the default user name and password you will be in the routers internal settings and you can then go to the wireless section and the wireless sub-menu and set your encrypted pass key (security key).
You can set a password for each frequency band but it would be best to use the same one for both.
You then wite down the pass key in case it's needed and you won't have to go into the router to get it. Don't forget to save your changes.