1. Explain it simply
(就要 / 快要 / 快 / 要) + verb + 了 means the action is about to happen very soon.
The final 了 is obligatory — never drop it.
When the sentence has a specific time word (明天, 下个月, 五点), you must use 就要……了; you cannot use 快要 or 快 with a fixed time.
2. Show examples
新年就要到了。
Xīnnián jiùyào dào le.
The New Year is about to arrive.
就要……了
火车快要来了。
Huǒchē kuàiyào lái le.
The train is about to come.
快要……了
明天就要考试了。
Míngtiān jiùyào kǎoshì le.
Tomorrow the exam is about to happen.
time word → 就要
快要下雨了。
Kuàiyào xià yǔ le.
It's about to rain.
final 了 required
3. Share a tip
Never forget the final 了 — it is what makes the sentence mean 'about to happen'. And when a specific time word is present (明天, 五点), use 就要……了, not 快要 or 快.