Not everyone can learn just by reading the book. There is a reason schools and teachers are how they're supposed to be, if students were supposed to just read the book and do the homework listed in the book and turn it in then what would class be? What are the teachers even there for? Many, if not most, people need to be explained something better than or even simply explained verbally to really understand and remember it.
Not in all cases, but in your example, I would say your teacher isn't doing the job they are paid to do. First try talking to the teacher, afterwards you can maybe try politely explaining it to your guidance counselor or a different teacher (not the principal right away, they might not have time to listen or look into it and it might seen a bit rude).