The second chapter (or "book") of Zhuangzi is widely considered one of the smartest, strangest, and most challenging philosophical works ever composed. It drives contemporary scholarship on Daoist thought, and has shaped many careers.
It is not easy to summarize the topic - in fact, the chapter was probably assembled from multiple shorter passages on a family of related topics. Those topics include knowledge, judgment, language, and ethics. The analysis proceeds at a very abstract level while staying rooted in everyday concerns: health, happiness, cooperation, and discovery.
Zhuangzi 2 is a particularly useful place for people to start learning about Daoism, if they bring a Western philosophical background. Some of the concerns are familiar: knowledge of cause and effect, personal identity, individuation, and normativity. But the response to these concerns is often intriguingly novel: thoroughgoing skepticism leads not to worry but to joy and release, for instance, and the best understanding of ethics is held to yield no ethical instructions whatsoever.
We will struggle through this text line by line - it is dense. Bring a hard copy if you have it; any translation will serve. Here are some online versions: