Or in questions: A hay B?

To offer a choice in a question, put hay between the options: Anh uống trà hay cà phê? Would you like tea or coffee? Nothing else is needed at the end: the choice itself makes it a question, so there's no không.

The options can be single words or longer phrases: Mình đi xe máy hay đi taxi? Shall we go by motorbike or by taxi? You'll often hear hay là: Ăn ở đây hay là mang về? For here or to go? It sounds a little more conversational, but it's fine in writing too.

The answer simply picks one: Cà phê. or Cho anh cà phê.

In a statement, "or" is often hoặc, especially in writing: Mình gặp thứ bảy hoặc chủ nhật. We can meet on Saturday or Sunday. Hoặc doesn't make a question, though; to ask someone to choose, use hay.

Hay has other meanings too. Between the person and a single verb, with no second option after it, it's "often": Em hay đi bộ. I often walk. Describing a movie, a song or a book, it's "good" or "interesting": Bộ phim này rất hay. This movie is really good. After a verb, it's "well": Cô ấy hát rất hay. She sings very well. When hay joins two options, as in đi xe máy hay đi taxi, it's always "or".