The going to form is used to talk about our intentions.
I am going to resign my job.
She is going to marry her boyfriend.
They are going to buy a new car.
I am going to ask her out.
We are going to complain to the police.
I am going to teach him a lesson.
I am going to start a business.
I am going to apply for that job.
Note that we use the ‘going to’ form when the action has already been decided and preparations have been made. The simple future tense, on the other hand, is used to announce decisions that we take at the moment of speaking.
Compare:
‘There is the doorbell’. ‘I’ll go.’ (NOT I’m going to go.)
‘I’m starving.’ ‘I’ll get you something to eat.’ (NOT I am going to get you something to eat.)
We also use ‘going to’ to talk about things that seem likely because there is outside evidence.
Look at the sky. It is going to rain.
Mary is going to have another baby in October.
The boat is full of water. It is going to sink.
The going to form may also be used to express an action which is on the point of happening.
Look! The cracker is going to explode.
The bus is going to leave.
The expression ‘about to’ can also be used to express the same idea.
The bus is about to leave.