Unsure about Time Capsule plus AirPort Express network

Assuming that you are using a recent operating system like Lion, Mountain Lion, Mavericks or Yosemite, or an iOS device like the iPhone or iPad, the setup wizard will practically do everything for you.

If the AirPort Extreme is new, connect the Ethernet cable from one of the LAN <--> ports on the Time Capsule to the WAN port on the AirPort.

If the AirPort Extreme has been used previously, then you will need to power it up for a minutes and hold in the reset button on the back for 7-8 seconds, then release and allow a full minute for the Express to restart.

Once you have the Ethernet cable connected, run the setup wizard and accept its recommendations. The only thing that you might have to do.....(normally you don't) if you have assigned a separate name to the 5 GHz network.....is go back after the initial setup and use AirPort Utility to check to see if you need to adjust this setting on the AirPort.

If you need a few tips on using the setup wizard, we need to know whether you will be using a a Mac or an iPhone or iPad to set things up.

Get the AirPort connected using Ethernet as mentioned above.

Click the WiFi icon your Mac, and look for a listing of New AirPort Base Station

Just below that, click on AirPort Express or AirPort Extreme, whichever you have

That will get the setup wizard going, and it will take a minute to analyze things ,then suggest that the AirPort will extend the Time Capsule network, similar to this illustration......

Type in a name that you want to use for the new AirPort device.....Extreme, or Express, for example

Click Next

Watch the next screen carefully to confirm that the AirPort is being set up to extend using Ethernet. That will confirm the correct setup.

When you see the message of Setup Complete, click Done. That's it.

If you want to use the iPhone.......

Go to the home screen

Tap on Settings

Tap on WiFi

Look for the listing of Setup a New AirPort

Tap on AirPort Express or AirPort Extreme

Everything else is the same as above

The setup wizard should have transferred over the separate 2.4 GHz and 5 GHz names that you were using on the Time Capsule automatically to the AirPort.

Was that the case?

Nice work to get things set up. Thanks for posting back.