Congratulations! If you've read this far through the book (editor's note: this comment only really applies when we've actually finished writing all the TODOs so far) then you've been introduced to all the fundamental components of angr necessary to get started with binary analysis.
Ultimately, angr is just an emulator. It is a highly instrumentable and very unique emulator with lots of considerations for environment, true, but at its core, the work you do with angr is about extracting knowledge about how a bunch of bytecode behaves on a CPU. In designing angr, we've tried to provide you with the tools and abstractions on top of this emulator to make certain common tasks more useful, but there's no problem you can't solve just by working with a SimState and observing the affects of
As you read further into this book, we'll describe more technical subjects and how to tune angr's behavior for complicated scenarios. This knowledge should inform your use of angr so you can take the quickest path to a solution to any given problem, but ultimately, you will want to solve problems by exercising creativity with the tools at your disposal. If you can take a problem and wrangle it into a form where it has defined and tractable inputs and outputs, you can absolutely use angr to achieve your goals, given that these goals involve analyzing binaries. None of the abstractions or instrumentations we provide are the end-all of how to use angr for a given task - angr is designed so it can be used in as integrated or as ad-hoc of a manner as you desire. If you see a path from problem to solution, take it.
Of course, it's very difficult to become well-acquainted with such a huge piece of technology as angr. To this end you can absolutely lean on the community (through the angr slack is the best option) to discuss angr and solving problems with it.