I have to learn Russian.I have to bring textbooks.I have to answer teacher's questions in lessons.I don't have to take exams every year.I have to do homework.I don't have to read newspapers and magazines.I don't have to take photos.I have to wear a school uniform.I don't have to join school clubs."Have to" обозначает "обязан", например, I have to do my homework.- Я обязан делать домашнее задание."Don't have"означает не обязан, но не ставит категоричное "нет"- можешь делать, если хочешь. Например: "I don't have to take exams every year"-Я не обязан сдавать экзамены каждый год.