The Universe

While the universe is a complex construct, I, Malacor Father of Conjuration and Chancellor of Magic from the Arkayne, will here take you, the reader, on a journey through its creation, concepts and global history. This will require a certain degree of knowledge of nomenclature to which I will first inaugurate you.

Nomenclature

Plane : A plane is the denomination for a world with its own laws of Nature & Magic, materially separated from other planes by magical means. Therefore one cannot travel from one plane to another without the usage of magic. They are often referred to as a plane of Oblivion as they were created from the Oblivion of before. Furthermore, such a plane is often created by a deity, be it Aedra, Daedra, Mundra or Divine (see The Pantheon for more on the deities), and can differ greatly from the laws of Nature mortals are used to.
Mundus : Either the deity Mundus, third son of the Allmighty one Orsus, or the mortal plane of Mundus, which Mundus created from his own energy, is referred to. Most often the reference goes to the plane since Mundus has vanished after his creation, some even say becoming his creation in the process.
Mortal Soul : From Mundus' own essence he formed the concept of the mortal soul. Basically the mortal soul comes down to Mundanian energy with its own free will. While other deities have tried to mimic Mundus' creation, never has the free will really been conjured. As such harvesting the energy of the mortal soul is much sought after by both deities and mortals, birthing the field of Necromany.
World : Although interchanged by some with plane, a World is technically a sub-plane within a certain plane. A world does however adhere to the laws of Nature & Magic of its governing plane and as such is placed lower in the hierarchy then a plane. A prime example is the world of Nexus (the afterlife) within the plane of Mundus, or the world of Arkis (where we the Arkayne reside).
Veil : The magical barrier situated around Mundus, omitting entrance to Mundus from alien beings such as the Aedra and Daedra. A tear is made in the Veil upon plane-traversing. As such when one travels to another plane of Oblivion, otherworldly entities may enter Mundus through the hole torn in the barrier.
Void : The (de)materialized space in between the planes of Oblivion. Some parts of the Void are inhabited by sentient creatures, among them for instance the Queen of Blades: Priscilla of Blades. Those that inhabit the Void are referred to as demons (for more information on the Void, see Void).

Global History

0th Era: Creation

Upon the embodiment of Mundus and the birth of the Mortal Soul, the world of Mundus entered its first Era: Creation. During these times the world's elements were formed, as well as the planets inhabiting the plane. After a long time our mortal race, the Arkayne was birthed. Although the Arkayne were very rich in detail and history, about which I could write hundreds of texts, I will not dwindle from the subject at hand. After thousands of years of civilization, we the Arkayne decided to create our own World within the plane of Mundus, to shape it to our every liking. As such we left Mundus with a group of the wisest, strongest and most powerful of the Arkayne. Unbeknownst to us were the consequences this would bring upon Mundus, namely the dawn of the first Era: the Godwars.

1st Era: the Godwars

With our departure to Arkis we tore a large hole in the Veil, which allowed the gods to enter Mundus with their armies. The Godwars were ended by the re-installment of the Veil by Magnus, along with the institution of his laws of 'Plane-traversing and Magic'. It is due to the Godwars that many species that today inhabit Mundus, such as the 'Dovah' or 'Dragons' in common tongue, even exist within Mundus.

2nd Era: Age of Legends

With the Veil in place again, the servants of the gods that remained from the first Era became trapped in the plane of Mundus. After many generations these servants took up enough Mundanian energy to become mortals. Many of the common mortal races of these days were thus created during the second Era. Furthermore, this Era is known for its many heroic deeds, even giving rise to two divines: Arazir & Jack of Blades. It was ended by the (partial) materialization of the Void, achieved by the joint efforts of the Arcane Masters. 

3rd Era

The Era we are currently residing in, has not been named yet by us Arkayne as we are still debating whether Hokan succeeded in his dawning of the Fourth Era. The events that have come to passing in this Era are readily described by today's historians and the like. As such I will conclude my part on the history of the Universe.
All info was taken directly from Malacor's writing: 'Travel through the Planes of Oblivion'.