Explore the Nuclear Fallout
Once you access the launch system and break the encryption on the launch codes, you will be able to select the location of the nuclear explosion. When the nuke hits the target and explodes, if you have the right gear you may now explore the fallout and fight high level mutated enemies. This will reward you with plenty of high level loot.
Launching a Nuke
Now that you been shown the steps necessary to launch a nuke, the only thing left to do is to complete each of the steps listed. The Surveillance System Terminal located in the Command center can provide you the locations of each item necessary to launch the nuke, but it is up to you to decipher the encrypted code and fight your way through the defenses.
Note: The Nuclear Silo code pieces will expire after One Week. If you fail to collect all 8 code pieces before a week, you will have to re-collect any codes that have expired.
When you collect all the necessary pieces and launch the nuke, you will complete the quest I am Become Death and finish the Enclave story line.
Now that you know how to launch the Nukes hidden in the Silos in Appalachia, you can repeat the collection process to continue launching nukes for high level loot and enemies.