1、am/ is/ are going to + do和will/ shall do.

Which paragraph shall I read first?

2、be going to+动词原形或地点，表将来

What are you going to do tomorrow?（明天你将要做什么？）

Look at the dark clouds, there's going to be a storm.

3、be+不定式表将来，表按计划或正式安排将发生的事。

We are to discuss the report next Saturday.