Looks like you need a _lot_ of foundational stuff first. Page 17 has already jumped into multiple integrals, which at least when I was studying undergraduate calculus 30 years ago wasn’t covered until Calc IV. The appendix rushes through a lot of stuff you’re apparently expected to already have had some exposure to like Taylor series, probability density functions, eigenvalues and eigenvectors… it looks like you’d need at least an undergraduate (if not a graduate) level math degree before you could make much sense of the contents of this book.