Once you've read this, pick up Harchol–Balter's book Performance Modeling and Design of Computer Systems: Queueing Theory in Action. It's a really good introduction to the depth of this topic, and you'll come out with superpowers you didn't have before.
This review is not so nice: https://emptysqua.re/blog/review-queue-theory-book/
Even if you just read the first few chapters of this you will not come out unchanged.
I don't think this is a good resource for an intro tbh. Unless you are interested in proofs and have some probability basics covered, it feels quite dense.
I liked Principles of Product Development Flow a lot more because it was easier to digest, although it's a different application of queuing theory.