What happens during a surgical operation?

I am going in to hospital on Tuesday for a hernia operation. I haven't had an operation before, and am just wondering what's involved. I have been told that I will be in and out the same day, and that I will be in theatre for about 45 minutes under general anaesthetic, but what else do I need to know? How long will I be drowsy for after the operation? Will I be nauseous or in pain? Will they do any other tests before or after the operation?