If you want to unlock Psi-Abilities, you will need to gather what are called Psi Points. You can get these through two main ways, the first being by visiting shrines and the second is completing quests.
That said, the first method is straightforward to do as you can find psi shrines all over the game world, and by visiting them, you will get one psi point. Psi Shrines will also look like small tents, you can't miss them.
However, just going to the location will not be enough to get your free psi point. For that, you must walk up and interact with the shrine at least once. After this, you will get your one free point from the shrine, which can be used to get some cool magic abilities.
Next you will need to complete various quests, as some will give you one point that you can use, and you also might run into some events that might wind up rewarding you with a point.
Once you get some Psi points, you will be able to unlock some cool abilities, but some will be locked to your aura type. In the event of this, you will need to raise your aura level to either dark or light, depending on the psi ability. You can do this by performing various evil or good actions in the game.