Hi, Ting Lan! They are used depending on the context of the situation you're referring to: "teacher/ instructor"- someone who teaches, especially in a school. "tutor"- a private teacher who teaches a single pupil or a small group. "mentor"- someone you trust to advise you. (synonyms: advisor, confidant, counsellor) "supervisor"- a person who oversees and directs someon's work (like a manager) Good luck! ;)