The Setup Guide that came with your Time Capsule covers this pretty well......but.....here you go.
Keep the Time Capsule and Fios router separated by 6-8 feet, or a few meters to minimize the chances of wireless interference effects that might occur between them.
Connect an Ethernet cable, which must remain permanently connected at all times, between one of the LAN <--> ports on the Fios router to the WAN "O" port on the Time Capsule.

Power up the Time Capsule for a minute or two.
Click the WiFi icon at the top of the Mac's screen and look for a listing of New AirPort Base Station. Just below that, click on Time Capsule. The example below shows an AirPort Extreme, you will see Time Capsule on your screen.

Or, if you are using iPhone or iPad for the setup.......On the Home Screen, tap on Settings, then tap on WiFi. Look for the listing of Setup a New Base Station and just below that, tap on Time Capsule
That will start up the setup "wizard", which will take a minute to analyze the network, then show a screen like this. except that you will see an icon of the Time Capsule:

Network Name.......Enter a short, simple name that you want to call the wireless network. Mine is TWNDB, for example.
Base Station..........Enter a short, simple name that you want to call the Time Capsule. Mine is TC, for example
Password...............Enter a password that will be used for both the wireless network and device password
Verify......................Verify the password
Click Next
The wizard will set up everything for you. When you see the message of Setup Complete, click Done.
Now you should be able to choose the name of the wireless network that you specified and enter the password to connect. You can also connect your Mac directly to one of the LAN <--> ports on the Time Capsule if you want to establish a wired connection.