How it began
As far as is known, premor began. That's it. It simply began and has yet to end.
In all honesty, this is how both magic users and astronomers have described it. The famous astronomer Ingerlocke wrote in their essay, "There's a clear date for when premor began if you know where to look for it; Year 09, day 36, at 1:48 am give or take a few milliseconds. There was no warning, no ordeal over creating it. It just began and was everywhere as if it always had been there".
And this true. Many tests and even trips back in time have been taken and every one of those has shown the energy simply was not there, then was there. As if some hand had scribbled colour onto a page.
What it is
Premor is the background energy of the multiverse. Some worlds know it as dark energy, but it is far more than they describe it as. Premor is around and in everything. It exists everywhere at once throughout time, making up a huge portion of the worlds. It appears to keep balance to chaos, and thrives around dying stars, black holes and mysterious tears. With its connection to itself throughout time, it seems as if it could be an answer to swift time travel. Though it's an almost untamable power few can comprehend, many people have attempted to.
What you can do
Premor is the most powerful of the three usable magics. In essence, it can do pretty much anything the weilder wants. From the smallest party trick to building an entire planet. Weilders have been known to build cities and towns and roads using it.
It takes a long time to learn how to control this magic properly, but once mastered it's an incredibly useful tool.
Dangers
As with any magic, there are dangers to using it. Those who have yet to learn to control it have reported parts of the world being ripped apart before them, small black holes forming, a star being born and many other strange and sometimes wonderful accidents. A big enough "Spell" going wrong could result in city, country or even world destruction.
Another danger is the use of any premor, no matter how small. This magic cannot be created or destroyed; it can only move places. By using the magic to create, say, a firework, the amount of energy needed to make that firework is taken from elsewhere in the multiverse. It's not necesessarily taken from nearby or the same timeframe, it could be taken from an entirely different world several years from then. This has caused the collapse of buildings and roads and many other things as the energy is suddenly gone from beneath it. On one occasion it has even destroyed a Ring.
Effects on the user
Although for a few years after beginning to practice using premor is fine, it gradually changes the user. They become hungry, but not know what for. Empty and longing for something yet never being able to tell what it is they want. Using premor satisfies this for a while, but it returns even stronger after use, again and again. This goes on until the weilder cannot stand it any longer. Many premor users have taken their own life because of it.