Subject + 留下 + 了 + Object
The verb 留下 (liúxià) means 'to leave behind,' 'to stay,' or 'to remain.' It can describe physically leaving something in a place, or abstractly leaving an impression or mark. It combines 留 (to stay/keep) with 下 (down/behind) to emphasize something remaining after departure.
他走的时候给我留下了一封信。
Tā zǒu de shíhòu gěi wǒ liúxià le yī fēng xìn.
When he left, he left me a letter.
这部电影给我留下了很深的印象。
Zhè bù diànyǐng gěi wǒ liúxià le hěn shēn de yìnxiàng.
This movie left a very deep impression on me.
你先走吧,把钥匙留下就行。
Nǐ xiān zǒu ba, bǎ yàoshi liúxià jiù xíng.
You go ahead; just leave the keys behind.