While we cannot know what is actually being planned in the NK military. The announcement from NK as reported by the Washington Post was that they would fire four mid-range ICBMs, into the sea about 30-40km from Guam.
This would be done by mid-August (though no date was given).
The original source of this is kcna, the North Korean offical news source. They say:
The KPA Strategic Force is now carefully examining the operational plan for making an enveloping fire at the areas around Guam with medium-to-long-range strategic ballistic rocket Hwasong-12 in order to contain the U.S. major military bases on Guam including the Anderson Air Force Base in which the U.S. strategic bombers, which get on the nerves of the DPRK and threaten and blackmail it through their frequent visits to the sky above south Korea, are stationed and to send a serious warning signal to the U.S.
The plan is to be soon reported to the Supreme Command soon after going through full examination and completion and will be put into practice in a multi-concurrent and consecutive way any moment once Kim Jong Un, supreme commander of the nuclear force of the DPRK, makes a decision.
The execution of this plan will offer an occasion for the Yankees to be the first to experience the might of the strategic weapons of the DPRK closest.
Explicitly speaking again, the strategic weapons which the DPRK manufactured at the cost of blood and sweat, risking everything, are not a bargaining thing for getting acknowledgement from others and for bartering for anything, but they serve as substantial military means for resolutely countering the U.S. political and economic pressure and military threat as what has been observed now.
Further details via yonhap news:
The North's Strategic Force said that it is "seriously" examining an "enveloping strike" of Guam with four Hwasong-12 missiles and will finalize the plan by mid-August, according to the Korean Central News Agency (KCNA).
Just one day after the North outlined its strike plan, it unveiled details in a tit-for-tat bellicose rhetoric against Washington which says all options are on the table.
The North said that the missiles will cross the sky above the Shimane, Hiroshima and Koichi prefectures of Japan and fly 3,356.7 kilometers for about 18 minutes before landing 30 to 40 km away from Guam.
The plan was devised in a bid to "interdict the enemy forces on major military bases on Guam and to signal a crucial warning to the U.S.," the report said in an English statement. The launches will be upon its leader Kim Jong-un's order.
The quotes in that report are yonhap news's translations of a statement on NK television from Kim Rak-gyom, commander of the Strategic Forces.
Now while this would not be directly hitting the island, it is still well within the Guam exclusive economic zone, and indeed within the Contiguous zone surrounding Guam. It is part of the sea that the US claims exclusive rights over. It is not part of the high seas, and so could be seen as a strike on US territory. There is no indication in the published statement that NK would put a warhead (nuclear or conventional) on the missile.
There is also concern about the accuracy of the ICBMs that NK has, and the consequent risk of an accidental hit on the island.
The declared purpose of the proposed strikes is to prevent the US Navy forces based in Guam from being used, and to demonstrate the effective military strength of NK.
