千万【qiānwàn】

千万 makes a request or a warning urgent: "whatever you do", "be sure to". It goes before the verb, after the subject if there is one, and most often before a negative – 别, 不要, 不能.

With 要 or 记得, it is a strong "be sure to".

Only for advice and warnings

千万 points at what someone should or shouldn't do next. It can't describe what already happened, or what you yourself did.

• × 我千万没告诉他 → 我真的没告诉他
• × 他千万来了 → 他一定会来的

As a number, 千万 is "ten million". The adverb always sits before a verb, so the two don't get mixed up.