While it's a great book, I think it's very intimidating for a newcomer to the field. (I assume, without meaning anything pejorative by it, that a lot of the HN interest in mathematics comes from amateur mathematicians with varying backgrounds.) Humphreys (https://www.cambridge.org/core/books/reflection-groups-and-c...) or Grove and Benson (https://www.springer.com/us/book/9780387960821) is probably a better introduction.