A Nickel history of the Inhumans for those who want to know:
Long ago an advanced race of beings called the Celestials visited earth and did genetic experiments on humans resulting in the creation of two species: The Eternals (good, perfect) and the Deviants (evil, monstrous). The Celestials also performed similar experiments across the galaxy including on the alien race, the Kree.
Sometime later, the Kree came to earth and discovered Homo sapiens. They knew from their own genetics about how the Celestials had unlocked genetic potential within their own race, and they figured out that humans were capable of undergoing the same process. So the Kree began running their own experiments and called the resulting super humans The Inhumans. Unlike the Celestials, who created the Eternals and Deviants as a pure experiment and didn't get involved in their development, the Kree not only tampered with the Inhumans, but also let them know why they had been created. They wanted the Inhumans to battle against the Kree's alien foes, the Skrulls.
The Inhumans rebelled against being token pawns in the Kree-Skrull war, and instead created their own society, separate from the Kree and separate from humans as well. At one time this society was located on the Blue Area of the Moon, and another time it was hidden in the Himalayas. Currently, the Inhumans are without a kingdom and are scattered across the earth.
The Inhumans aren't born with powers or mutations, they are born looking very much like ordinary humans. But at a certain age, all Inhuman children undergo Terregenesis: a ceremony where they are exposed to Terrigen Mists, a chemical which unlocks their genetic potential. The results are usually superpowers or physical mutations or both. A very few become grotesque and are seen as the remnants of the Deviant bloodline in their race.
The Inhumans are led by a King and Queen, Black Bolt and Medusa. Black Bolt's power is a voice that is powerful enough to shatter a mountain with a whisper, so he almost never speaks. He leads through example and through the words of his wife, Medusa. Medusa's power is telekinetic hair, which she can manipulate as if it were alive. I.e. she can wrap people up in it, use it to grab stuff, etc.
The Imhumans are pretty aloof with humans, they don't want to get involved in petty human wars and such, but they have developed friendships and relationships with certain superheroes. So occasionally the Inhumans find themselves aiding and working alongside earth's heroes for a common good cause. Notably, the Inhumans are on good terms with the Fantastic Four, one of them married and had a child with the Avenger/X-Man Quicksilver, and Black Bolt is a member of the Illuminati, a secret organization of the top minds of the Marvel universe.
Oh and one of the Inhumans is a giant dog who can teleport groups of people where ever they need to go. Yeah, you heard me. His name is Lockjaw and he's awesome.