The《山海经》is kind of a zoologist’s manual of magical creatures: it describes where they live, what they look like, what they eat, and sometimes, how they came to exist. This particular passage is the origin story of the famous 精卫 jīng wèi, a mystic bird that spends its time trying to fill up the ocean (填海) with sticks and pebbles.
But 精卫填海 is not just a story from antiquity, it has also become an idiom in modern times. Filling up the sea with pebbles is, obviously, a futile, pointless, and never-ending job, which is exactly what this phrase now describes. In other words, the 精卫 is the Chinese equivalent of Sisyphus from Greek mythology, the king cursed by Zeus to roll a bolder up a hill for all eternity, and “精卫填海” describes a similarly Sisyphean task. But sometimes it can have a positive meaning: dogged determination in the face of overwhelming odds.
Books written prior to around 1920 are mostly written in classical Chinese, which is kind of like Shakespearean English. Because this language can be difficult even for native speakers, classic texts are often translated into modern Chinese. The version of 《精卫填海》 that we’re going to read today is the modern Chinese translation of the classical Chinese.
There are a few proper names of people and places, which I’ve highlighted in the Chinese text. One god mentioned in passing here is 炎帝 Yán dì, the Fire Emperor, a semi-mythical figure from ancient history.
One note on grammar: this passage uses a less well-known definition of the character 为. In this case, 为 means “become” or “into”, so the phrase 化为 mean “transform into”.