This is a spoiler free description of both power systems. This will help you understand the core concepts and names used in the novel from the begining.
Cang Yun's Previous World
In Cang Yun's previous world power system's building block is Qi. Both mortals and immortals have a Qi sea below their naval in a spiritual level.
This world's power system is mainly divided into ten ranks.
Rank 1-5 = Mortals Rank 6-9 = Immortals Rank 10 = There is only one of them in the world.
This world uses arts which are powered by Qi and they are divided into ranks as well. Immortal arts also have special names.
Rank 1-5 = Arts Rank 6 = "Great" arts Rank 7 = "Immortal" arts Rank 8 = "Extremity" arts Rank 9 = "Supreme" arts Rank 10 = "Heavenly" arts
When someone use an art, they have to do the corresponding had signs. Then they have to say or think the art's name(Special name+Art's name) to fully use it.
Aurora world's power system
In this world people use Mana which is provided by the Mana core that spiritually exist below one's right chest.
This world has classes and everybody has to choose one before beginning their journey towards magic.
People in this world uses skills instead of arts.
This world's power system isn't divided into mortal or immortal realms and the skill ranks aren't divided either. But the ranks have special names.
Rank 1-5 = Mage Rank 6 = Arc Mage Rank 7 = Grand Mage Rank 8 = Wizard Rank 9 = Wizard King Rank 10 = (Doesn't have a name)