It is mainly a classic of Buddhist knowledge, which discusses people's thinking, psychology and emotion. It is a masterpiece of ancient "psychology". The Buddhist scriptures and treatises are the most difficult parts in Mahayana Buddhism. The scriptures are often very thick (for example, the Yoga teacher's "On the Earth" is as thick as two or three dictionaries), and the meaning is obscure. Even in Buddhism, there are always different opinions.
Master Xuanzang in the Tang Dynasty was a master of epistemology. Unfortunately, the theory that he only knew the truth (seeking truth from facts) spread in China was almost lost after only a few generations.
The main classics are Huayan Sutra, Shen Jiemi Sutra, Tathagata Merit Sutra, Mahayana Amitabha Sutra, Tathagata Sutra and Afterward Sutra, as well as Yoga Teacher's Land Theory, Advocating the Holy Religion Theory, Mahayana Solemn Sutra Theory, Concentration Theory, and Empathy Theory.
If you want to study systematically, most beginners will learn Shurangama Sutra and Shen Jiemi Sutra first, and then learn the above other classics according to their own interests.
If you don't want to study systematically, you just want to have a preliminary understanding. You can find "realistic" textbooks in various Buddhist colleges in China. These textbooks are concise and clear, especially suitable for beginners. When I was studying, I couldn't understand a question when I read the classics. Later, Master gave me a textbook that only knew knowledge, and I got it. Unfortunately, it was later given to a friend.