Open AirPort Utility
Click on the AirPort Extreme icon
Click the Wireless tab at the top of the window
IF.....you have a compatible modem.....the option to enable the Guest Network will appear. Name the network and assign a password and confirm.
Click Update to save any changes and the AirPort will restart in 30 seconds
If the Guest Network option does not appear, you have a modem/router, not a simple modem. Contact your service provider and ask them for a simple modem if you want to enable this feature.
Bob - Quick explanation
Bought a new Digital TV> Messed with the Wi-Fi settings through the TV and had to reset Airport Extreme to Factory Settings. Initially had Guest Network which has now dissapeared.
Looked for Edit button after pressing airport extreme and it is not there. I just seemy initial network and all the neighbors. Am I searching for the edit button correctly.
I also see - Join other networks, Create Network, Open Network Preferances...