I guess I need to consider learning Hangul
Now, given that the Russian observers claim it's freakin' huge, and supposed to yield about 20kT, and given that depending on whose numbers you like it actually yielded between 550 tons and 2 tons, and given that no one has detected any radiation at all (freakish unusual for even underground tests), I'm guessing that either it did not work as advertised, or it's a hoax.
It's also not suitable to mount on a missile or "sneak" into the United States like some commentators have suggested.
Best use--throw it on the back of a truck. Execute a conventional attack into South Korea, and if they take Seoul, park the truck in downtown Seoul, then negotiate.
More likely--keep containing North Korea, and eventually their population will eithe revolt, or starve to death. Either way, it doesn't matter.
What should be done immediately: Tell the North Koreans that any nuclear attack anywhere in the world that is not provably the work of another government will be assumed to be their bomb, and we'll turn South Korea into an island 20 minutes later. Mention to the Iranians that if they hold a test, the same rule applies to them. Yes, that means if one terrorist sets off a bomb anywhere in the world, we'll wipe out two societies.
Did you see that? No? That was me giving a rat's ass.