As a beginner, they don't plausibly understand anything. Understanding functions and variables is a deep topic that can take years to master. If it is possible to truly understand them and assuming human knowledge has reached the point where we understand functions completely - I feel confident we've got variables although even then it is hard to be sure. And that covers all of programming! I suspect in a large number of cases "admit when you don't understand something" is useless advice because the problem is they can't identify discrete chunks of knowledge to practice.
Even today I don't fully understand what a bus really is. I mean I sort of get that it is one or more (copper?) wires that carry information as electricity somehow but at no point do I remember anyone saying this explicitly in any of my education.
I've had to piece this information together in my head from multiple conversations. So now when I hear the word bus, I think a ribbon cable. Each of those cables can only send two states, high and low current and that's how I think of a bus because anything more advanced isn't something I can intuitively process at all.
So I'll just nod and smile when people talk about bus and I don't understand a thing.
