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。
下面做个简要的讲解。
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