Also, feel free to make explanatory notes to yourself in the margins of the pages of your textbook. A good way to improve your understanding of something is to pause periodically and reflect on it. If the answer is no, reread the material. It's also helpful to mark or underline key passages in the chapter. This makes you an active participant in reading and provides you with key passages to review for tests.
Some students prefer to mark or underline as they read.
Others prefer to read through the material, and then to go back and highlight the most important points. I prefer the latter approach, because I usually have a better idea of the key passages after I've read through the material. Mark only key passages or ideas. You reopen the book and find the number again. But this time as you close the book, you repeat the number to yourself, either silently or audibly.