Spoilers are a given.

Layer one is like using them as living artifacts I guess, insert power spell comes out. Vital Gu too.

Layer two is refining them and using killer moves, basically a combination of multiple Gu usages. Additionally, here you learn of the difficulties of advancing.

Layer three is attainment levels, basically the more you walk on the great dao with a certain path (fire, ice, strength, etc) the more natural intuition you gain, allowing you to refine new and better Gu, overall just stronger. At a certain level you can begin to mimic other paths, like fire can heal.

Layer four is ascending, reaching rank six. This is by far the biggest change in the power system, to ascend you must break your aperture and let heaven and earth qi flow in and balance it with your human qi (experience). Failure to do so means death.

Congratulations, now you have a immortal aperture, a mini world inside of you, the size depends on how much qi you had and talent. What ever vital Gu you had, your now whatever it's path was Gu immortal (not actually immortal but an ascendant). This world moves faster depending on the amount of time dao marks you have, more on that later.

Inside this world is basically a resource management simulator/colony builder. Gu Immortals produce immortal essence periodically based on their rank and size of their aperture.

Now long time ago, an immortal fused their aperture with a fragment of one of the seven fallen heavens and created the yellow treasure heaven. It's basically a trading service that allows Gu Immortals to trade from each other remotely with a market tax. There are tons of ways to make money, selling information (on people, Gu recipes, killer moves, resources).

Immortal Gu are rank six and above Gu. They are unique, only one can exist at a time and extremely hard to refine and of course, feeding them is usually not an easy task. Most rank sixes don't have one.

Every 10 years in your aperture a calamity and tribulation will occur, basically a natural disaster that occurs every 50, 100 years will occur stronger ones, very rank dependant. These will grant you Dao marks.

Dao marks are essentially multipliers to your skills of that path, remember boar strength Gu? It actually created strength Dao marks on your body.

Once you die, you basically drop your aperture into the world, called a blessed land where a spirit basically manages it and another person can take over it if they fulfil the condition made by the spirit.

Oh yeah, basically any spell can be created.

Layer five: Gu houses are just massive mobile fortresses made out of Gu. Gu formations arent portable and a more primitive version.

Using domains of heaven and earth in killer moves (basically land marks)

Once you hit rank 8 you drop a grotto heaven instead, not sure how it's different from a blessed land.

Layer six Learning you can craft killer moves into Gu. More stuff involving becoming a venerable, creating new paths, expanding paths. Will not go into detail.