I bought a high school English reading daily practice to improve my reading level, and cumulative words. But after doing it for a few days, I think this book is so difficult

This book is definitely not for you, don't read it again, it will hold you back. If you're not in a hurry, buy a Starfire English or Bookworm first, (mainly stories, these are synchronized with the grade level,) accumulating words at the same time, training the spoken language, reading, and developing a sense of language. You might want to start training with middle school English, junior year's, to get the foundation right. Otherwise, you will be entangled in this won't and agonizing, and finally affect your interest in learning English, put that book away. To make a suggestion, you can enroll in a New Concept English class, depending on the situation to choose a class, I am also so step by step to adhere to it