The key thing is doing the exercise problems; most textbooks have them at the end of each chapter. Yes, it takes time. Yes, you will struggle, and it's hard wor

The key thing is doing the exercise problems; most textbooks have them at the end of each chapter. Yes, it takes time. Yes, you will struggle, and it's hard work going through them. But it's really the only way to make sure you really understand the subject at a sufficient level vs. you believing you understand it because you watched some videos.