A lot of students have the same problem as you because they don't know how to get information from a textbook. It takes work.
I tutored a student once who paid me to read his textbook and explain what it was saying. He only did it once because I think he saw the process I went through. I didn't just read the book and immediately get what it was saying. Sometimes I had to flip back in the book and read some earlier material to learn definitions, etc. Other times, I'd read a few sentences, and I wouldn't know exactly what they meant. So I'd end up saying what I found confusing and asking him what the sentences might mean. I'd also offer suggestions on what the author might be saying, and every once in a while, I'd say something that connected to something he knew or heard in class. Then he'd explain that to me and I'd reread those sentences and paraphrase what I thought it meant based on the information he had provided.
It wasn't so much that he couldn't do this himself, but he just got discouraged when it didn't make sense to him right away. But he could see that I hit the same roadblocks he did, but I just didn't quit so quickly. I kept banging away at it until it made sense to me. That one tutoring session, I think, really opened his eyes to what level of work was expected of him in his classes.