how to apply The Feynman technique efficiently to effectively improve my learning in math and physics?
There are two key parts of the Feynman method: teaching and keeping a record.
The basic insight behind the first is that if you can teach something effectively then you know it well. Many professors have had the insight that &quot;I didn't understand X until I had to teach it&quot;. But if you are going to teach something complex to another person who has (much) less understanding, then you will probably need to resort to analogy and metaphor to get them into the correct mind set.
So, the application to the Feynman method is to form analogies about what you are studying, where the analogies are common (enough) and easy to recall.
But the recording part, using notebooks, is also essential, since writing down your insights engages the brain in a somewhat different way and that reinforces the physical changes (synapsis and such) that make deep learning possible.
So, one suggestion for using the method is to imagine someone, like one of your parents or siblings (unless they are also field experts) and imagine teaching some complex topic to them. Jargon and technical figures probably won't work, so you appeal to what they already know and come up with some analogies that will help them get started. But you don't just do this as a mental exercise. Write it down, as a lecture outline.
The other suggestion is that when you read and take notes (or listen to lectures and take notes) that you follow it up by summarizing those notes in a simpler form, say using analogies that will remind you of what you have just read. In fact, I'll guess that when you read something your mind is already working out some analogies. Record those. Having a &quot;faithful&quot; record (copy) of what you have read/heard isn't the same as learning. You need to engage the brain. Forming analogies and writing summaries are both good ways to make that happen.

There is more to learning that just the Feynman method, of course. This is why instructors give assignments and exercises.  Exercises help engage the brain in another way that is even more effective. It is also why cheating on assignments is counterproductive to learning. Reinforcement and feedback are keys to learning. The feedback is needed so that you don't reinforce incorrect things.