How can I study technical books so I actually retain and use what I learn?

Use active recall instead of just highlighting. After reading a section, close the book and explain the main idea in your own words, draw a diagram of how the pieces connect, and write a small example or program. For operating systems, try to connect each idea to a concrete behavior, such as what happens during a system call, process switch, or memory allocation.

Don’t rely on reading alone. After each chapter or section, try implementing the ideas in code and complete the related exercises or projects before moving on. Applying a concept forces you to understand what problem it solves and helps you recognize how it works in unfamiliar situations.

It’s fine to read through the whole book once to become familiar with the vocabulary and major concepts. Then revisit the difficult sections more carefully and work through the assigned problems or practice exercises. Technical subjects build gradually, so compare explanations across different books or resources when something doesn’t make sense.