Both “ở” and “tại” can indicate location, but they are used in different contexts.
“ở” is more casual and commonly used in everyday speech.
“tại” is more formal and often used in writing or official situations.
Tôi sống ở Hà Nội. → I live in Hanoi. (Everyday, natural)
Cuộc họp diễn ra tại văn phòng công ty. → The meeting took place at the company office. (Formal, official)
In daily conversation, use “ở”.
For documents, news, signs, or formal contexts, use “tại.”
Never use both together (e.g., ở tại is redundant and incorrect in modern usage).