Coding is not about understanding it’s about practice and consistency, it’s not comparable to high school courses, you will need to practice coding to be good at it and understand it, reading it and trying to understand only the theory is not the way. Download code complier in your computer and try to practice, especially; focus on algorithm and data structures. Don’t compare it to highschool courses. It’s like Being good at drawing doesn’t necessarily you will be good at architecture.