There are three subjects in the unified entrance examination for postgraduate mathematics, namely, one, two and three. Generally speaking, counting one is the most difficult. Number one includes three types: advanced mathematics, also called calculus; Linear algebra; Probability theory and mathematical statistics. I used to use Youku to download videos, where there are many resources. If the foundation is not very good, I suggest you don't read Tsinghua and Li Yongle at first. His lecture is really classic, but it is suitable for you to read it after you have a certain foundation. Cai Yonghua's is good, you can have a look. But the premise also requires you to have a basic concept of textbooks.

There are many chapters in advanced mathematics. The most important thing is differentiation and integration. There is no problem if these two concepts are clarified.