I finally got 8 nuke codes for a single silo today. So here is how the nukes work:
1) You first have to become a general within the Enclave, as this gives you access to the actual nuke silos
2) You need a nuke ID card and 8 nuke code fragments. The Enclave can help you locate the card and spawns with the nuke code fragments.
3) Once you have that, you can access the actual nuke silo. However, once you are inside, there is a lot of shit you need to do. Make sure you have computer hacker 3, as it makes it alot easier (unless you like fighting 20 minigun turrets at once lol). Hacker 3 will let you deactive entire floors of turrets and also the mini-boss robots (robo brains mostly, although there is a sentry or two inside in addition to the gutsys/assaultrons/protectrons).
4) Quick run down: I had to spoof a biometric ID card, then I had to repair a nuclear reactor in less than 3 minutes all while being attacked, then I had to run around destroying computer cores, then you later have to repair some computer cores, then when you finally get to the nuke command center, you have to guard 5 protectrons that actually prep the nuke for launch. Basically every step during this, you are being zerged by all sorts of robot security and the security program for the base will keep creating more. Once the protectrons prep the nuke, all robots in the facility go into standby mode and stop attacking.
5) You have to insert your nuclear ID card, then you have to enter the code. However, the code is a puzzle. Basically, every nuke code has a letter and number. The 8 letters spell a word, which gives you the sequence of numbers to enter. As a hint, inside the Enclave bunker, they are running a decryption program that gives you some letter placement hints for the various silos. You cannot see this later, so you need to make note of it/figure out the code word. The code word changes every week, but it appears to be the same across servers.
6) If the code is correct, then you can use the targeting computer. The game won't let you nuke the noob spots (Vault 76 and the surrounding towns). Every other POI is fair game. If you target a fissure, then it spawns the raid bosses.
I didn't have very good weapons, so I figured I would just target a normal city. I picked one with a bunch of people nearby, since I figured people would want to watch. When I launched the nuke, it told the entire server what I had done and advised them they had a few minutes to escape the blast zone. If you are in the blast zone when the nuke hits, you are vaporized instantly. You can stand outside it just fine.
When you enter ground zero, radiation is insane. The radiation levels slowly get lower over time, but you'll be chugging Rad-X and Radaway like a fiend even in power armor. Any radiation based perks are your friend. Pretty much the only thing that will let you function without getting mass rads is the hazmat suit, but you basically aren't wearing armor with that thing and stuff hits a lot harder.
So the nuked areas serve a couple purposes. One, the mobs there give MASSIVE xp. I got like 10 levels killing glowing bloated ghouls. Mobs drop certain special items. Also, the plants yield special flux items. If you have the green thumb perk, use that, since it gives you double plant harvests. Once you harvest/loot, the items will not remain indefinately. The flux especially will decay in less than an hour. To keep them perma, you have to stabilize them. Once you get enough plant harvests and special mob drops, find a chemistry bench and there is a nuked flora category. This stabilizes the flux and it won't decay at this point. The crafted flux is used in end game crafting/powerful mods, including upgrading your underarmor/vault suit. The raid bosses apparently drop plans/etc.
It's possible to do the silo and a regular city solo, but I basically used all my meds and ran out of .308 ammo and kept having to repair my melee lol. Although later on, when I joined another server, someone nuked Whitesprings and it spawned a level 80 scorch beast, which you aren't soloing (or at least not without using 1k rounds of ammo lol).