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.

That is also a good book containing a few practical applications of queueing theory, but it won't do anything to help you analyse your own systems on a more fundamental level.