Nowadays most WiFi Routers have a button either on the top or the side that allows you to set up a new connection without having to enter your WAP o WEP password on your mobile device. This is often called Push-Button-Method or One Push Setup, it varies( you can search for WPS on google to learn more about this).

On N9 go to Settings--->Internet connection--->Connect To internet--> Wait for your network to appear-->Select it,
If the Push-Button-Method is supported/allowed by your router it will give you that option along with another PIN method option, or you can skip Easy Configuration entirely by setting up you preshared WAP or WEP key.
Now, you must push the button on your router (or activate the function via the web UI) and then select the Push-Button-Method on N9 as well, this will create the connection for you.

The one problem you might encounter with this is that not every router has this option enabled because of security reasons (when this happens the N9 skips this entirely and only gives you the option to enter the WEP/WAP Key) and there are still some that don't support it but most linksys i have seen do support it.