The Philosopher's Stone is an alchemical product with great abilities which even The Dark Lord sought to have, to provide him with a body.
 Creator/s and Creation
Nicolas Flamel, the only known maker of the stone, lived to the age of 665 using the stone while his wife, Perenelle Flamel, lived to 668, also using the stone. It is unknown how he created the stone but it is known that he is perhaps the greatest alchemist of all time.
The Philosopher's Stone was an alchemical product with great powers, being able to turn any metal into gold, and also providing the Elixir of Life, which, if drank regularly, extended the life of the drinker until regular consumption stopped. It was able to provide a bodiless yet earthbound being a body, this being the reason Lord Voldemort sought it.
The stone was a key element in the first book, as implied by the title. It was kept in Gringotts Wizarding Bank, in Vault 713, until removed by Hagrid under Dumbledore's orders before the Hogwarts term started. Later that day, Quirinus Quirrell broke into Vault 713 for Lord Voldemort, however the stone was gone and Voldemort was forced to keep a "closer watch" on Quirrell.
After Hagrid took the stone to Hogwarts, Dumbledore somehow concealed it in the Mirror of Erised, one of his creations. The stone was kept there until at the end of the year, until Harry Potter managed to once again thwart Voldemort, and the stone was destroyed with it's creators blessing.
 Outward Appearance
The stone was a bright ruby red colour which other than this was like a shiny, small and ordinary rock.
 Other Information
It was not mentioned that the stone/elixir could provide Voldemort with a body in the film version of Harry Potter and the Philosopher's Stone.
It is unknown whether the stone prevents death from injury and illness or whether it just prevents death from old age.