dung khong co gi
When does one use da and when vang?
Generally speaking, "vâng" is "yes" in the Northern Vietnamese dialect, and "dạ" is southern.
How do you say "yes" to someone younger in the south?
Use ừ if you are addressing a younger person
"Ừ" or "ờ". Friends use it among each other, too. It's really weird if you use "vâng" / "dạ" around friends. xD
You can just say có