TIme capsule Wifi extension

The Time Capsule cannot connect to a third party network using only a wireless connection, if that is what you are trying to do.

If you have another Apple AirPort router providing your WiFi signal, then the Time Capsule can be set up to connect and extend the WiFi network.

Apple designed their "extend" option as a proprietary option that would only work with other Apple AirPort routers.

So, the first question here would be.......do you have another Apple WiFi router that is providing your wireless signal?

Extend wireless must be to another Airport Wireless router. What other Airport are you using?

And you must NOT use ethernet .. if you do a loop will result.