The world of DND is dynamic and complex, spanning multiple planes and multiple universes. There are a total of 6 cannon planes, and the world of Dungeons and Dragons can take place in any kind of realms, as long at the DM has the imagination to pull it off!

The Astral Plane
  The Astral plane is the plane of thoughts and dreams, and it acts as a kind of void between the inner and outer planes. Time is meaningless, and many years can pass in the blink of an eye. The plane is described as a Silver sea above and below, dotted with pools of light that represent portals to the other planes.
The Etherial Plane
  The Etherial Plane is a foggy, strange dimension that borders the other planes. On it's outsermost reaches, the plane overlaps with the other planes, allowing for one in the ehterial plane to view what is on the plane it overlaps. The Etherial plane is frequented by Ether cyclones, strong forces that have the power to rip portions of the plane apart and scatter all who are caught up in them to the Astral plane.
The Feywilds
  The Feywilds are home to all of the fairy kind. Wildly tall trees, plants made of Crystals, and counless tiny creatures fill this magical world. The Feywild Mirrors the material Plane, sharing many of ts features, and expanding them into fantastic form. The Fae always deligtful creatures, and the Feywild is also home to the sinsiter, trickster fey that cause chaos in the Feywilds more sinsiter outer reaches.
The Shadowfell
  the Shadowfell is a cold, unyielding world that is filled with shadow and death. The sky is a permanent, sunless stone grey, and the world is filled with ominous ruins. The denizens of the shadowfell ae those that have seen death: Vampres, zombies, mad scientists, and ghouls, along wih a plethora of monster baddies. Like the Feywild, it is possible to slip into the Shadowfell by means of finding a portal, and they would find a world warped in similar fashion to the material plane, but extra gloomy.

The Inner Planes
  THe Inner Planes Consist of the four elemental planes that provide the material for all the physical realms: The plane of Earth, Water, Fire, and Air. Forming a massive ring, each plane embodies its element, and where they mingle near their edges there are signs of life.
  - The Elemental Plane of Air is a Massive, Open expance of sky that is unfettered by land. Aarakokra, or bird peole, live in this magnificent plane, soaring aloft on the insanely strong winds that swirl around the never ending sky.
  - The Elemental Plane of Fire is the Epitomy of hot: The Cinder Wastes dotted with rivers of Lava dominate the landscape, and the sky is choking ash. Fire Elementals and a number of other species wander across the scorched and agressive landscape.
  - The Elemental Plane of Earth appears as a titanic mountain range, with peaks so tall no air can be found around them. Within these great mountains are cities of precious metals, and caves dotted with massive magical crystals. as the plane of eath touches the plane of water, a terrible swamp expands, consuming everything in its thick, murky, depths.
  - Finally, the plane of Water Expands as an endless ocean, Whose shallows are filled with merfolk and other water-borne creatures, and whose dark depths are occupied by kracken and a number of terrifying god-like creatures. as it borders the plane of Air, the region turns cold and gradually coalesces into a massive glacier that forms the dividing line between the two planes.
The Outer Planes
  The Outer realms are more metaphysical in nature, as apposed to being physical places. They are the realms of the Gods, and the places where the Order and the Chaos of the universe are established. The outer planes have many layers, and each plane has an alignment, and in DnD, there are 9 alignments, each relaying an attitudes towards Rules and Self:
  - Lawful: Rules are more important than Comfort.
  - Neutral: Rules and Comfort are Equally important
  - Chotic: Fun is more important than the rules.
  - Good: Others are more important than me
  - Neutral: I am as important as others
  - Evil: I am more important than others
  That leaves 9 possible alignments, and each has outer plane associated with it:

  | Lawful | Neutral | Chaotic
  --- | --- | --- | ---
  Good | Lawful Good (LG) | Neutral Good (NG) | Chaotic Good (CG)
  Neutral | Lawful Neutral (LN) | True Neutral (TN) | Chaotic Neutral (CN)
  Evil | Lawful Evil (LE) | Neutral Evil (NE) | Chaotic Evil (CE)

  Those planes are:

  Plane of existence | Alignment
  --- | ---
  The Seven Heavens of Mount Celestia | LG
  The Twin Paradises of Bytopia | LG, NG
  The Blessed Fields of Elysium | NG
  The Wilderness of the Beastlands | CG, NG
  The Olympian Glades of Aborea | CG
  The Heroic Domains of Ysgard | CN, CG
  The Ever-Changing Chaos of Limbo | CN
  The Windswept Depths of Pandemonium | CN, CE
  The Infinite Layers of the Abyss | CE
  The Tarterian Depths of Carceri | NE, CE
  The Gray Waste of Hades | NE
  The Bleak Eternity of Gehenna | NE, LE
  The Nine Hells of Baator | LE
  The Infinite Battlefield of Acheron | LE, LN
  The Clockwork Nirvana of Mechanus | LN
  The Peaceable Kingdoms of Arcadia | LN, LG

  Many of these planes can only be reached by portals, and the connections between the planes are hard to find, and even harder to exploit. Many of the outer planes, with the exceptions of Mechanus, Arcadia, Celestia, Bytopia, and Elysium are terrible places where life must fight to survive.
Other Planes
  Beyond the outer Planes lies the Far Realm, a place where the geometery of reality starts to fall apart. Massive and terrible creatures Exist here, Whispering terrible truths to all that would listen.
  There are other planes that are created by spells. These planes are called Demiplanes, and are come and gone when their usefulness ends. They are hard to find without help from their creators, and they are as mysterious and dynamic as the sorcerers that Cast them into being.

The World of D&D is strange and, in a lot of ways, hard to imagine. The Great thing about D&D is that the game is not limited by these rules: If the story calls for an entire elemental plane of bees, then by golly, that can exist. The Entirety of the D&D game exists in a massive Multiverse that spans countless sessions ans players, and the universe is as complex as the players who exist in it.