The Feynman Technique
Take a blank piece of paper and write that concept at the top of the page.
Write out an explanation of the topic, as if you were trying to teach it to a new student. When you explain the idea this way you get a better idea of what you understand and where you might have some gaps.
Whenever you get stuck, go back to the source material and re-learn that part of the material until you get it enough that you can explain it on paper.
The goal is to use your words, not the words of the source material. If your explanation is wordy or confusing, that’s an indication that you might not understand the idea as well as you thought – try to simplify the language or create an analogy to better understand it.
Then you are forced to simplify the language :)