At first you have just two powers at your disposal, both of them being more for body-to-body access.
Several early party quests will give you the opportunity to learn again, much more powerful but also more difficult to evolve.
Powers, like equipment will be classified into 5 categories of rarity:
A legendary power will usually be more powerful than an epic power, provided you use it well, but it will be much more difficult to mount it.
The powers can be improved in 3 ways:
Improving the level of power by surpassing gold.
By improving your equipment.
If you have the level of spell required, you can then unlock a new rank, to place additional runes, these runes to improve the spells or change the use.
Runes can be found all as equipment, power parchments and equipment gems.