When The Sundering occurred the violent birth of the Aether Sea was the first of many catastrophic events. The Aether was formed when the Ethereal plane collapsed into the elemental chaos creating a turbulent endless sea of magical energy
Mages through mental exertion are capable of shaping the raw energy of creation into physical being. Any attempts to bring any aethershaped object into a material plane solar system will cause it to dissipate. Because of these difficulties large scale or permanent aethershapes are almost unheard of.
The Aether is not a place of physicality so much as it is one of pure creation and consciousness. Since its creation natural inhabitants referred to as Wyldlings have spring into being. These beings exist in a strange state of pure consciousness with the ability to physically manifest themselves in the Aether - and even in material planes if the conditions are right.
Beyond Wyldlings there are also those who live as nomadic traders between material planes who spend more of their time residing in the Aether than any material plane. There are also some extreme cases of individuals who whether they are researchers, or other have some other purpose, choose to live primarily (or completely) within the Aether.
Needless to say life within the Aether is challenging at best. Inhabitants require extensive facilities for food and air creation, and any raw materials they require must be imported from material planes - or require a capable mages able to maintain an aethershape. In addition to the extensive infrastructure required just for a basic living there have also been cases of strange mutations occurring in those who spend extensive amounts of time within the Aether.
Travel through the Aether Sea generally occurs in large vessels equipped with Rune Engines. While these engines have existed well before The Sundering newer advances are capable of achieving exceptionally higher rates of speed within the Aether compared to material planes.
Resting outside normal Aether space are the Pattern and the The Labyrinth . These two primal forces of magic reside outside any known vassals ability to travel to (if they can even be reached at all), but the energy that emanates from them can be tracked by Mages. Depending on the proximity towards either pole the energy from one or the other will be stronger, allowing a basic ability to navigate with an Aether Compass.