Trying to learn a level maths

I decided to try and learn a level maths under aqa.

Thought I'd try learning from a book.

Bought Cambridge University a level mathematics for aqa (new linear spec) 2017.

I'm literally pulling my hair out. It's like this book is designed for someone who already knows a level maths.

I'm pretty competent at gcse level mathematics. But this.... It just presumes a great deal of knowledge about maths that I don't have.

It offers almost no explanation on how to do anything it's asking for. I've searched for the answer on reddit forums. And the solution to this question, which is on the second page btw, is incredibly advanced for my level!

What am I missing here? Is what I'm trying to do even possible, or is this just poor teaching design?