Mount Doom or in Elvish 'Orodruin' is a volcano on the plateau of Gorgoroth in the east of J.R.R. Tolkien's fictional land of Mordor, within sight of Barad-Dûr, the Dark Tower stronghold of Sauron. High up on its side are the Cracks of Doom, seemingly an entrance to the fires below the mountain, and where the One Ring was forged. Casting the One Ring into the Cracks of Doom was the ultimate goal of the quest of The Fellowship of The Ring. Frodo Baggins, Samwise Gamgee and Gollum (or Sméagol) suceeded in traveling across Mordor, and scaling the mountain, under the very Eye of Sauron.
From the eastern side of Mount Doom a causeway ran across the plain of Gorgoroth, over a mighty bridge and on to Barad-Dûr itself. Sauron channeled the lava across the plain to his tower, presumably to fuel mighty forges in the tower itself.
It seems that it more than a natural volcano, or at least the Dark Lord Sauron is able to use his magic to manipulate it: Boromir says 'Smoke rises once more from Orodruin that we call Mount Doom'.
Probably Sauron used Mordor as his base, precisely because this powerful volcano was what he needed to forge the One Ring to bind all the other lesser rings to him, and ensure his victory over Elves, Dwarves and Men.