To master a topic, pretend you are teaching it to someone. Use simple language and analogies. If you stumble, study the topic some more, then try again.
Richard Feynman was a physicist who received a nobel prize for his work in quantum electrodynamics. He was notorious for asking his mathematicians to explain concepts in simple language to test their understanding.
Here his unique technique to learn new materials:
Step 1. Choose a topic you want to understand and start studying it. Once you know what it is about, take a piece of paper and write the topic at the top of the page.
Step 2. Pretend you’re teaching the idea to someone else. Write out an explanation on the paper while you describe them out loud. Like this you get an idea of what you understand and where you still have gaps. Whenever you get stuck, go back and study. Repeat that process until you can explain it.
Step 3. Finally do it again, but now simplify your language or use an analogy to make the point. If your explanation ends up wordy and confusing, that’s an indication that you do not understand the idea well enough. If that happens go back until you have mastered it.
It is the process of thinking about an idea while teaching it that make the method so effective. Once you can explain an idea with simple language and create graphic analogies, you have deeply understood it and will remember it for a long time.