Past tenses

There are none. A Vietnamese verb has one form, and "past" is a matter of context and, when needed, a marker in front of the verb or a particle at the end. Where English has to choose between ate, was eating, have eaten and had eaten, Vietnamese chooses whether to mark the time at all.

Nothing, if the time is already clear

A time word makes any further marking redundant:

Hôm qua tôi đi Huế. — "Yesterday I went to Huế." Năm ngoái chúng tôi mua nhà. — "Last year we bought a house."

This is the normal way to talk about the past. Adding đã to these sentences is correct and a little heavy, like saying "yesterday I did go".

đã: before the verb

Đã marks that the action is done — past, or perfect, as English would have it:

Tôi đã đọc cuốn sách này. — "I read / have read this book." Anh ấy đã về. — "He has gone home."

rồi: at the end

Rồi "already" at the end of the sentence marks completion too, and in speech it usually replaces đã rather than joining it:

Tôi ăn rồi. — "I've eaten." Xong rồi. — "Done." Tôi đã ăn rồi. — "I've (already) eaten." — both, for emphasis.

Rồi answers the question chưa? "yet?": Ăn cơm chưa? — Rồi.

đang + past time: was doing

Ongoing action in the past is the progressive marker đang with a past time reference:

Lúc đó tôi đang ngủ. — "At that moment I was sleeping." Khi anh gọi, tôi đang ăn. — "When you called, I was eating."

vừa / mới: just

Tôi vừa đến. / Tôi mới đến. — "I've just arrived." Tôi vừa mới ăn xong. — "I've only just finished eating."

từng: ever, used to

Từng (or đã từng) marks experience — "have ever", "once used to":

Tôi từng sống ở Sài Gòn. — "I used to live in Saigon." / "I have lived in Saigon." Anh đã từng ăn phở chưa? — "Have you ever had phở?"

Passive of misfortune: bị

Things that happened to you — badly — take bị before the verb or adjective; good things take được:

Tôi bị lạc. — "I got lost." Xe bị hỏng. — "The bike broke down." Tôi được tặng quà. — "I was given a present."

There is no pluperfect

"Had done" is đã with the time relation left to the words around it: Khi tôi đến, anh ấy đã đi rồi. — "When I arrived, he had already left." The two đã / rồi markers and the khi clause carry the order of events; the verbs carry nothing.

If you speak Korean

Đã is -았/었 as a separate word, and as in Korean it is dropped whenever a time word makes it redundant. Từng is -ㄴ 적 있다: tôi từng sống ở Sài Gòn = 사이공에 산 적 있어요. Bị for things that happen to you is 당하다 / -게 되다 in spirit.

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