Be动词有三个，am，is还有are。我用am，你用are，s跟着他她它，复数全部都用are。如果遇到过去时，was来把am，is替，were来把换掉动词are。
初中英语动词知识点：Be动词的定义
do和be动词的用法区别。
Be 动词就是(am，are，is)句子中如果没有实意动词(例如：write，buy)之类的动词，就直接在主语后面加Be动词。而如果是句子中有实意动词，那么如果你要改为一般疑问句，就要借助DO(do也称为助动词)，例如：I study.
改为一般疑问句：Do you study ?
顺口溜：be氏三朵花， am， is还有are，
我(I)恋am， 你(you)恋are，
is跟了他(he)她(she)它(it)，
单娶is， 复娶are。
详细讲解：
英语的be 动词是个用法比较复杂的动词。复杂的原因有两点：
1、除了原形的be 之外，对于不同人称代词以及单数名词和复数名词，be 会有各种变化形式和缩写形式。概括一下有七种形式：be，am，is，are，was，were，been，being。它们与人称代词和名词单、复数的搭配关系是：
现在时 I am，you are，he/she/it/ is，we/you/they are;名词单数、不可数名词用is，复数用are。
缩略式 I'm，you're，he's，we're，you're，they're
否定缩略式 I'm not，isn't，aren't
过去时 I was，you were，he/she/it/ was，we/you/they were;名词单数、不可数名词用was，复数用were。
否定缩略式 wasn't，weren't
过去分词 been
现在分词 being
2、在句子中，be有两种主要作用：一是作为系动词(The Linking Verb)，本身可以作用谓语动词;二是做为助动词(The Auxiliary Verb)，与谓语动词一起构成各种时态和被动语态等。
初中英语动词知识点：Be动词的用法
一、be 动词做系动词
1、系动词+表语”的结构
当be 动词做系动词使用时，主要构成“系动词+表语”的结构，在句子中做谓语。表语可以是名词、形容词、副词、介词短语等。例如：
The man is a science teacher.
Mary's new dresses are colourful.
Mother is in the kitchen now.
I have been there before.
They shall be here at 10:00 tommorow.
That can't be true.
You are not being very polite.
Your brother is being very annoying this evening
2、be 动词的一般疑问句，方法是把be 移到主语前面，也可说成是移到句首。
Is the man a science teacher? Yes, he is. / No, he isn't.
Are Mary's new dresses colourful? Yes, they are. / No, they aren't.
Was mother in the kitchen then? Yes, she was. / No, she wasn't.
Were you at home the day before yesterday? Yes, I was. / No, I wasn't.
Was she late this morning? Yes, she was. / No, she wasn't.
3、be 动词用在特殊疑问句
在特殊疑问句里，be 动词仍然移到主语前面，但特殊疑问句是以特殊疑问词开头的，所以be 动词只能说是移到主语前面，或者说是在特殊疑问词的后面。例如：
Whose bike is broken? Xiao Ming's bike is.
Who was singing in the room? Mr. Zhang was.
Where are you from? I am from Wuhu.
What class were you in? We were in Class 2.
How old is Tom? He is ten.
4、be 动词的否定句
be 动词做谓语时，它的否定形式是在be 后加not，并且可以缩写。例如：
It is not sunny today.
Tom and his friends are not in the park.
You were not nine years old when I went to the university.
He was not often late for his class when he was a student.
I wasn't here yesterday.
My parents weren't at home last Sunday.
5、be 动词的祈使句
be 动词的祈使句有肯定和否定两种形式。肯定形式是以be 动词开头，而否定形式或强调句形，要加don't 或do。例如：
Be careful!
Be a good boy!
Don't be silly!
Don't be a fool!
Do be obedient!
Do be careful.
二、be 动词做助动词
助动词be 有两个基本用法，一是与谓语动词一起构成各种时态，二是构成被动语态。
“be + 现在分词组”成各种进行式时态。例如：
Tony's maid is washing his new car.
The children are playing in the field.
Samuel was eating when I came in.
We have been living here since 1959.
This time next day they will be sitting in the cinema.
三、注意事项
英语句子中，为了表达时态或被动语态的需要，常常会出现几个助动词连在一块儿使用。也就是说，助动词be会和其它助动词一起使用。这时候，整个句子的一般疑问句和否定句，就不一定是对be 进行变化了，而是以第一个助动词为主进行变化。即哪个助动词在先，就以它为主进行变化。例如：
[肯定句] All the wonderful birds can be found in our Bird Park. (助动词有两个：can be )
[疑问句] Can all the wonderful birds be found in our Bird Park? (移第一个can)
[否定句] All the wonderful birds can not be found in our Bird Park. (在第一个can 后加not)
[肯定句] I have been there before. (两个助动词：have， been )
[疑问句] Have you been there before?
[否定句] I have not been there before.
[肯定句] I shall be having my supper at six tomorrow evening. (两个助动词：shall， be )
[疑问句] Will you be having my supper at six tomorrow evening?
[否定句] I shall not be having my supper at six tomorrow evening.
四、助动词be，无词义，辅助主要动词一起在句中作谓语动词。用法如下：
1. be+doing：构成进行时态，有现在和过去两种进行时态。如：
The girls is reading and copying the new words now.
Young Tom was always asking questions and trying out new ideas.
2. be+going to do，表示“打算或将要做某事”，be有现在和过去两种形式。如：
We are going to plant trees in the park.
I didn’t know if she was going to come here.
3. be+to do，表示“按计划安排将要做某事”。如：
The new shop is not to be opened till next Monday. One night an angel came to
Mary and told her that she was to have this special boy.
五、there be
there be句式为：there be+主语部分+状语部分，表示“某处存在某物”，be常用现在时，过去时和将来时等。如：
Oh, cool! And there are many things to see. There is even a deer park in Sanya.
There are about 80 pyramids in Egypt.
Will there be a football match in your school next week?
六、实义be
可以将be视为实义动词，因为它具有实际的词义，如“成为;做;发生;举行;逗留;到达”等。如：His daughter wants to be a doctor for animals in her twenties.Kates birthday party
will be at half past six this evening.Jim has been in China for
morethan two years, but he has not yet been to Yichang.