Strong or formal command: hãy + verb

Hãy before a verb gives a firm or formal instruction: Hãy chọn câu trả lời đúng. Choose the correct answer. You'll see it in instructions, on signs and in adverts, and hear it in speeches: Hãy gọi cho chúng tôi ngay hôm nay! Call us today!

With chúng ta in front it means "let us", the way a speaker addresses a crowd: Chúng ta hãy cùng nhau cố gắng. Let's all do our best together.

In conversation, hãy sounds stiff, like a teacher or a public notice. To ask a friend to sit down, say Em ngồi đây đi or Em ngồi đây nha, not Em hãy ngồi đây. People do use it when they want to sound serious, in a heartfelt plea: Anh hãy nghe em nói. Please, just listen to me.

So hãy is the written and public way to give a command. In everyday speech, đi at the end urges someone on, nha asks nicely (in Hà Nội, nhé), and cứ tells someone to go ahead without worrying.