Hello, I am not very confident about my English expression, so I will answer your question through the translation software. The character you use, Yutu, is the pet of the goddess Chang 'e in Chinese mythology. Her initial possessions are a musical instrument, a pipa, and a tool, a medicine pestle. Pipa cannot be used at the beginning of the game. You need to find an island shaped like a crescent moon in the map, and in the center of the island is the moon palace where the NPC Fairy Chang 'e lives. Enter the moon palace and give the fairy Chang 'e some items to unlock the music score before you can play the pipa. The pestle can be used as a weapon or in the bottom of the synthesis table on the left side of the game. Every time you use it, you need to put fresh vegetables and fruits and other items in the grid and consume the hunger value. Different items in the grid have different effects, which can restore your hunger SAN or life.
In addition to this character, you can right click yourself to escape the ground to avoid damage from the night, but will quickly consume the hungry SAN, the ground will have debuff in rainy days and soon after the rain when the ground is wet
I hope it helps you understand this character

As a bonus, you can use a flower petal to make a moon moth to guide the direction of chang 'e's island

Thank you very much your explanation was quite clear! I watched some youtube videos but the pipa wasnt mentioned and Im very happy to know the name of the instrument now! I wil try using the mortar and pestle again! I failed before. You have been very helpful!!