be是一个多功能动词，在初级英语里可见四种用法：
功能一，系动词be
be为连系动词，中心词义是"是"，句型为"主＋系＋表"结构。be的形式常用am, is, are(现在式)；was, were(过去式)；will/can/may/must be(助动词/情态动词＋原形)；have/has/had been(助动词＋过去分词)等。如：
To help animals is helping people.(一般现在时)
The twins were very busy yesterday.(一般过去时)
It will be sunny tomorrow.(一般将来时)
She has been ill for over a week.(现在完成时)
功能二，助动词be
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+done：构成被动语态(主语是动作的承受者，done必须是及物动词)。如：
Tea is grown in my hometown.(一般现在时的被动语态)
This building was built three years ago.(一般过去时的被动语态)
Our classroom has been cleaned and tidied already.(现在完成时的被动语态)
How could this kind of cakes be made in your home?(含情态动词的被动语态)