打开 + 门
The verb-object compound 开门 (kāimén) means 'to open the door' and is a common everyday expression. Since 开门 is a separable verb-object compound, other elements like 了 or 着 can be inserted between 开 and 门. It can also be used figuratively to mean 'to open up' or 'to start business.'
有人敲门,你去开门吧。
yǒu rén qiāo mén, nǐ qù kāi mén ba.
Someone is knocking at the door; go open it.
这家店每天早上八点开门。
zhè jiā diàn měitiān zǎoshang bā diǎn kāimén.
This store opens at eight o'clock every morning.
她把门开了一条缝,往外看了看。
tā bǎ mén kāi le yì tiáo fèng, wǎng wài kàn le kàn.
She opened the door a crack and peeked outside.