The letter to the teacher should include the title, opening remarks, content, ending, honorific words and signature. In the opening remarks, you should address the teacher politely and show your identity. You can talk about what you have learned from the teacher and the influence of the teacher on yourself. You can also ask questions related to the teacher or discuss specific topics. Finally, you can express your gratitude again and express your expectation for further communication or guidance from the teacher. You can end this letter with polite words and sign your name and date.