All of it, all gone: verb + hết

After a verb, hết means "all of it, until nothing is left": Em ăn hết rồi. I've eaten it all. Compare xong, which you know: ăn xong is "finished eating", while ăn hết is "ate it all up", with nothing left on the plate.

With an object, hết goes right after the verb, before the object: uống hết ly nước (drink the whole glass of water), làm hết bài tập (do all the homework), đọc hết cuốn sách (read the whole book). Rồi at the end says it's done.

With more than one person, hết after the verb means "all of them": Tụi nhỏ ngủ hết rồi. The kids are all asleep. Mọi người về hết rồi. Everyone has gone home.

Two other uses look similar. Before a noun, with no verb, hết means "run out of": hết tiền, out of money. At the end of a negative sentence, it means "at all": Em không biết gì hết. I don't know anything at all.