Magic gifted from one to another

Usually gifted from deities, so a user essentially gets celestial abilities, which are very powerful

Can be as small as never tripping over yourself or as big as moving the very earth.

The limit of the power is determined by the being who gave it, and they can take it away if they choose, so one has to be careful.

Neither. When a person strikes a deal to be given power, they let the full extent of their intention be known, whether good or bad. As long as they continue to hold true with their original words, they can use their new power as they see fit.

It can depend on where they got their power from. Some gods are quite common to see gifting their followers power, while others have more of a reputation for being hard to win over. So, to strike a deal with those gods is typically seen as a big deal.

Due to usually being gifted power from a celestial being, the person will need to have a good loyalty to that being. But, more than that, each god needs to decide whether the person has the potential and drive for the power, so it goes on a case by case basis.

Nothing really has to be learned, other than a deep knowledge of whatever source you are getting the magic from.