The way you call people depends on your age and their age.
If they are male:
- You think that he is younger than you:
+ a bit: you call him "em", and you are "anh"
+ He is a child: you call him "cháu", you are "chú"
- You think that he is older than you:
+ a bit: you call him "anh", and you are "em"
+ he is the same age with you uncle: you call him "chú" or "bác", you are "cháu"
- You think that he is the same age with you: you can call him "ấy", "bạn", and you are "tớ", "mình"
If they are female:
- You think that she is younger than you:
+ a bit: you call her "em", and you are "chị"
+ She is a child: you call him "cháu", you are "chú"
- You think that she is older than you:
+ a bit: you call her ", and you are "cháu"
+ She is the same age with you uncle: you call her "cô" or "bác", you are "cháu"
- You think that she is the same age with you: you can call her "ấy", "bạn", and you are "tớ", "mình"
All things I tell you above is the calling in social communication. In Vietnam, if he or she and you are kinship, you will have other way to call.
My English is not very good. I hope you can understand what I mean ^^