Bagua (Eight Trigrams in English) is very important in Chinese from the ancient time and very popular in Chinese now. It's about spiritual power, cultivation, body and mind transcendence. You may often encounter Eight Trigrams in almost Chinese games (Gujian 3, Xuan Yuan Sword 7, ...)

At the core, there are 2 primal elements which are Yin-Yang. They stand for dark-light, positive-negative, true-false, yes-no. Everything in Heaven-Earth had maintained balance. Surrounds them are Yin-Yang combinations.

Please note: I had no intention to discuss much about Eight Trigrams. Just give an explanation how to solve in-game puzzle.

In short, you may consider Eight Trigrams as a 3 bit binary system on a computer in modern world which is 2^3=8. That's why it had octagon shape. Optional, Chinese can use their expanded system by combining 8 Eight Trigrams which is 8x8=64 maximum (2^6=64 - 6 bit binary).

You may look at the following Zhaodan Spring layout:
There are 4 pairs which negative each other and stay at the opposite positions. So they don't follow 1,2,3... order in decimal. This is how to read them.

When you were the internal space of Zhaodan Spring, entering the big mirror will teleport you to 1 of 8 Dragon Seal Buidings. At this moment, you started the puzzle. Look down where you're standing. There is something on the floor. You have to read letters on it.

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Once you realized what it is, you need to activate the Dragon head and move its Seal Building to the right position.

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You may take a look to see it right or wrong.

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Now, you may know what to do.
Deal with 7 Dragon Seal Buildings remaining in a similar way until you complete the puzzle.

They are located at Tianshi Sect's Divine Pagoda at the time the main story leads you there.
There are many ways to do. The idea is making them all face out and then complete the puzzle. It took the following steps.

First, we had the Turtle faced out, activate the Phoenix and turn it face out.

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The Turtle and Phoenix faced out already, next, activate the Unicorn and turn it face out. The Dragon also faces out at the same time.

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Final, all statues faced out, at this moment activate the Turtle and turn it face to the core. The others will turn too. The puzzle done.

The puzzle isn't too difficult, once you realized what it is, you would know how to do it.
The puzzle is the main plot of the story, game let you skip it if you didn't mind it.
It's awesome game anyway. Hope you enjoy it as well.
Happy playing.