To be 的用法可以写一本书.
To be 是不规则动词,你必须熟练掌握它的各种形式：
am , is , are , was , were , is being , has been , should be , could be , would be , might be , shall be , will be , can be , must be , need to be ...
轻易得到的东西你不会珍惜,所以我就不多说了.
它的用途主要有：
1. 系动词,相当于“是”
例如：The flower is red .
2. 表存在,
例如：China is in Asia .
3. 表判断（是/否）,
例如：Are you there ? Yes , I am .
在学习过程中,你还会发现它的许多用法.对 to be 的掌握程度（不仅仅是背下来）是你英语水平的标志之一.