how can I find correct network settings for my 3rd generation time capsule?

If you have a router it should be bridge..

If you have a modem then the TC should be router.

If you already have wireless then you can put the TC into reinforce it.. but you cannot extend another brand wireless router.. the TC must connect by ethernet to the main router or modem.

What else do you need to know?

Have you tried simply plugging it in and let the airport utility setup wizard discover the setup and auto complete?? If not try it.. gets it right 8/10.

Apple's setup and configuration "wizard" will almost always do a very nice job of analyzing the type of modem that is being used on the network and assign the appropriate network settings to the Time Capsule based on the wizard's network detection capabilities.

So, if you are concerned about "correct" network settings, it would make sense to first confirm that the Time Capsule has been setup to work correctly with the type of modem that your Internet Service Provider has supplied to you.

Could you provide the make and model number of the device that you call your "modem"?

Your post did not tell us anything about what operating system the Mac or PC that you will be using to check settings, so we would need that information as well to begin the process.