Hades was the Greek god of the dead in Greek mythology, he and his brothers Zeus and Poseidon overthrew their father, the Titan Cronos, and divided lots to decide which part of the world each would control. Hades was awarded the underworld and the dead.
Hades was also the name of the Greek underworld, where the spirits of the dead went. According to Homer in the literary work The Odyssey, Odysseus sailed upon the River Styx to speak to the dead to gather information in his quest to return home to Ithaca.
While Hades was known as the abode of the dead as described by Homer, there were also differing sections. Most of the dead seemed to mill around in no particular distress, though in no way enjoying this existence either. In Tartarus, though, punishment was the order of the day: for example Tantalus was suspended from a fruit tree the boughs of which would move if he tried to pluck a morsel from the tree; while suspended above a pool ever thirsting but the water never met his parched lips.
Another section of Hades was known as the Elysian fields, where the souls of those who were particularly noble or heroic were sent.
There were five rivers in Hades: Acheron, Styx, Phlegethon, Cocytus and Lethe. According to the Odyssey, the first four of these were joined: Cocytus was a branch of Styx, and Cocytus and Phlegethon both flowed into Acheron. 
Notes & References
- Homer: The Odyssey:Book 11
- Homer, Odyssey 10. 513