Studying from bad material

I have an upcoming exam, and my school has instructed us to study from a specific textbook. The problem is that this textbook is poorly written. The author uses bizarre sentences that often make no sense, and the content is severely outdated. I can't rely on other resources because the exam is entirely based on this textbook, and I feel like I'm wasting time looking up every single concept that pops up. I tried to push through and slowly work my way through the text, but it's incredibly frustrating and demotivating. Does anyone have any tips or advice on how I can get through this?

This is my first post on this subreddit so please go easy on me