[markhkim]

Congratulations on graduating high school. That's quite exciting, and I'm sure you'll love university.

The about page states that the book is for "an intermediate level (i.e., after an introductory formal logic course)." It'd be advisable to look elsewhere first if you don't have any exposure to propositional logic. For example, the first eight chapters of MIT's Mathematics for Computer Science textbook should be sufficient: https://courses.csail.mit.edu/6.042/spring17/mcs.pdf

The standard tip for reading mathematical texts is twofold: always try to come up with a proof before reading the one supplied in the text, and never ignore the problem sets. As Pólya famously put it, mathematics is not a spectator sport.