If you want to become and auror or anything else that involves the dark arts, your never going to do that if you don't know how to defeat them. I am a first year but I do know a thing or two about defense against the dark arts. If you don't already go to the defense against the dark arts class, I suggest you enroll. But if you want something a bit more basic and easier for you to understand, I suggest you read this book because this is going to come in handy.