All clauses in English have at least two parts: a noun phrase and a verb phrase: 
所有英语句子里最少包括两个部分：名词和动词。

But most clauses have more than two parts:
但几乎所有句子多于这两个部分：
 

The first noun phrase is the subject of the sentence:
第一个名词部分是句子的主语：

The children laughed.

John wanted a new bicycle.

All the girls are learning English.

She put the flowers in the vase.

English clauses always have a subject:
英语句子里一定会有主语：

His father has just retired. Was a teacher. He was a teacher.

I’m waiting for my wife. She is late.

… except for the imperative which is used to give orders:
除了用于发布命令的祈使句：

Stop!

Go away.

… and for "soft imperatives" like invitations and requests:

Please come to dinner tomorrow.

Play it again please.

If we have no other subject we use "there" or "it" as subject. We call this a ‘dummy subject’:
如果没有其他主语，我们用there 或it 作为形式主语。

There were twenty people at the meeting..

There will be an eclipse of the moon tonight.

It’s a lovely day.

It’s nearly one o’clock.

I have toothache. It hurts a lot.