extend network with two airport extremes

I am using two Airport extremes to extend my WiFi signal. They are NOT connect with each other through cable. I am doing it wirelessly.Do I select the setting "extend a wireless network" on both the main Airport Extreme and the extended Airport Extreme? I am trying to have my Wifi signal to be stronger throughout the house and also to reach my patio. I currently have the extended Airport Extreme set to OFF Bridge. I have green lights in my Airport Utility on both units, but my Wifi signal doesn't seem any stronger on the patio. I have them about 30 ft. apart from each other.