Please, do me a favour: làm ơn + verb

Làm ơn before a verb means "please", literally "do (me) a kindness": Anh làm ơn nói chậm lại một chút. Could you please speak a bit more slowly? It goes after the person's word, or at the start of the sentence, and the request follows.

It's for asking someone to do something, often a stranger, and it sounds polite and a little formal: Chị làm ơn cho em hỏi, bưu điện ở đâu? Excuse me, could you tell me where the post office is? For "please don't", add đừng: Làm ơn đừng hút thuốc ở đây.

Said firmly, it can also sound fed up, just like an impatient English "please": Làm ơn nói nhỏ chút! Please keep it down!

It isn't the everyday "please" for ordering or asking for things: in a café you say Cho em …. With people you know, giùm after the verb is the friendly way to ask a favour: Anh mở cửa giùm em nha. Xin makes what you say humble, and mời invites someone to do something. On notices and from shop staff you'll see vui lòng: Vui lòng chờ một chút.