To add a bit of useful material to this community, I'm going to try making regular posts of grammar and language points. This is the first of what I hope will be many more.
Basic personal pronouns: Ông: "Grandfather", used for men over 50. Bà: "Grandmother", used for women over 45 (women get married and have kids at a younger age). Anh: "Big Brother", used for young men. Chị: "Big Sister", used for young women. Cô: "Aunt/Girl", used for young girls. Can also be used for young women, but it's kind of formal. Also used for female teachers. Tớ: Used to refer to yourself when you are talking to a close friend of the same age. Cậu: Used to refer to a close friend of the same age. Cụ: "Great-grandparent", used for very old people (around 70-80 and up) Cháu: "Grandchild/niece/nephew", used for young people talking to old people (if the older one is addressed as aunt/uncle/grandparent/etc. then the younger one is cháu). Em: "Younger sibling/child", used for people who are younger but not young enough to be your children. Also used to refer to students when they speak to their teachers. Thầy (Thày): "master/teacher", used to refer to male teachers and monks. ấy: "that", added after a pronoun to make it third person. It can't be used with pronouns that are exclusively first person, such as "tôi" and "tớ".