I think it's pretty normal and not even a problem to not understand everything your first go-around with some new tech.

I really wouldn't expect anybody to actually understand the modern web after one course. These things take time, experimentation, and deliberate practice before they will really sink in.

Moreover, you will always have to try to understand things at some level of abstraction if you want to be productive in any reasonable amount of time. To understand the entire stack of hardware, network, OS, browser, programming language, frameworks, and application code is at-least a decade-long journey.