一般将来时的基本结构是:am/is/are/going to+do.那am/is/are/going to在这充当什么角色?do呢?

be going to do 表将要做什么，至于是用am is are 是要根据主语来定的，主语是一人称单数就用am ,例如：I　am going to wash my clothes . 主语是三人称单数用is ,例如：He is going to buy a book.主语是复数就用are ,例如：They are going to play football .
do 代表后面的动词 ,如例子中的wash，play ,buy !

am going to do or will do
am 只用于I
is 用于she,he or it 单数主语
are 用于they,you ,we 复数主语
do 是动词的原型