It was morning. We heard knock on a door.

那天早上，我们听见有人敲门。

The little Klaus knocked on a door of a farmer's house near by.

小克劳斯敲了敲一户农民家的门。

For example, you knock on a door when you want to enter someone's house.

例如，当你想进入某人的房子时，你敲门。

He knocks on a door and the guy opens up and says what do you want?

他敲开一家人的门，有一个人出来了，问他：“你干嘛？”

He knocked on a door, said something quietly to the person who opened it, then walked upstairs.

他在一扇门上敲了几下，小声和来开门的人咕哝了几句，便走进去上了楼。

So, " knocking on a door" would sound something like – something like that.

所以，“敲门”听起来像——像那样。

It's a cool, fun feeling to be able to knock on a door, and be like " Hey, my name is Zach, " I'm a medical student.

敲门的感觉很酷，很有趣，就像“嘿，我叫扎克，”我是一名医学生。