Hell is an alternate plane of reality, traditionally accessible only by those of demonic heritage, beings of a higher order and those whose souls have been barred from entering the gates of Heaven or Purgatory.
During the "Day of Judgment", a fallen angel named Asmodel took control of the Spectre and sought to bring Hell on Earth. In the process, he used his powers to extinguish the Hellfire itself, and effectively freeze Hell over. A team of heroes including Superman, Zatanna, Faust, Firestorm, The Atom, Enchantress and Deadman were sent deep into Hell's bowls to reignite its flames. They were successful, but it required an action of true evil, and Faust was forced to slit Enchantress' throat on the spot. In doing so, he forfeited the soul he had recently gained through his own redemption as a hero.
In Hell, an ordinary human feels the worst feelings simultaneously: sadness, fear, pain. Hal Jordan, a Green Lantern Corps member (an intergalactic police whose members presumed doesn't know fear) was terrified with a brief stay in Hell . Hell is very scary, but demons are already accustomed and LIKE the place. Due to a effect of time dilation a day in Hell equals one minute of passage on Earth. In Hell, the landscape seems to change as someone walks. A place to be reached may seem like a few feet away, so in moments be far away again. 
In Reign in Hell the Infernal Dominion is divided up into several Provinces, all of which having a ruler. All Rulers bowed to Neron. The Nine Provinces included Pandemonia, The Odium, The Gull, Praetori, Internecia, Ament, Labyrinth, Err, and Purgatory.
Hell is a debased reflection of Earth, so as Earth became more technologically or socially advanced so does Hell. During the events of Reign in Hell, the Underworld is thrown into a massive conflict as Neron sees a rebellion from Lord Satanus and Lady Blaze.
Neron soon found that this rebellion was more dangerous than others, for the twin demons were offering the damned something he never could: hope of release. Recognizing what would happen if the damned rose up against him, Neron has Lilith summon all demons on Earth to return to Hell and aid him. This proves futile, as the rebellion triumph, and Blaze proclaims herself as the Devil after defeating Neron and betraying her brother.
The hierarchy of Hell has changed several times over the centuries, the leader of which has always assumed the title of Devil. The most well-known Devil is Lucifer Morningstar, the second fallen Angel and the supreme ruler of Hell for many centuries. When Lucifer fell from Heaven, it was revealed that the First of the Fallen was cast out long before Lucifer and had already been ruling Hell, although to First of the Fallen was no match for Lucifer's power, allowing Lucifer to take over. When the great Darkness of creation threatened all existence, a civil war erupted in Hell and the realm was split into a triumvirate. Eventually, Lucifer grew bored with his position and retired to Earth with his consort Mazikeen. Neron then assumed a predominant position in Hell.
The main currency of Hell are souls. Living human beings (or other sentient beings), through rituals, make pacts with demons to gain power, wealth or etc. The demons have between them a kind of "stock exchange" of souls, to set the price of the souls. When the person who did the pact die, their soul is then belong to the demons whom they negotiated.
A sold soul can be use as fuel for the spells of a demon. Souls can also be use as raw material to create hellish furniture at Odium manufacturers and factories. Souls can be freely traded with other demons much like the money of Earth; however, at the time the mortal sells their soul, he/she can do so only to a single demon. John Constantine once managed to outwit three demons to cure his cancer, since they were so eager to take the soul of the occultist who did not previously consulted, so John got his healing without losing his soul.
Sometimes, extremely evil humans who have been sentenced to the Hell can be promoted and gain demonhood. 
- Fallen Angels
- Anton Arcane (former human)
- Baytor (formerly)
- Brandor the Pit-Rider
- Demons Three
- Ernst Focke-Wulf von Raddell (former human)
- Etrigan (formerly)
- Lilith, Mother of all Abominations
- Mazikeen (formerly)
- Mnemoth (formerly)
- Ran Va Daath
- William Scumm (former human)
The Damned Souls
- It has been established by the Super Buddies that it is possible to get a cell phone signal in Hell. At least with Verizon.