Page 266 - Teaching English as a Foreign Language for Dummies 2009

Chapter 16: Feeling Tense? Sorting Out Verb Tenses
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Expressions typically combined with this tense include: for ages, for over (a week, two days and so on) and when plus a verb in the present simple tense.
Talking about ‘To be going to’
‘To be going to’ is not a tense as such but is an expression that shows you intend or plan to do something in the future. It sounds far less spontaneous than the future simple. Compare these sentences:
I’ll watch TV tonight.
I’m going to watch TV tonight.
The first sentence is used more often when it involves a new choice or decision: The party has been cancelled. I think I’ll watch TV tonight.
The second sentence gives the impression that you’d thought about the matter previously:
I’m going to watch TV tonight. I always watch the soaps on Mondays.
You can also use was or were going to to show that something was intended or planned in the past.
Getting the form right is easy! It’s the verb ‘to be’ in the present simple, then going to and then a verb in its infinitive form without the to.
I am going to do something.
You are going to do something. He/she/it is going to do something. We are going to do something. They are going to do something.
‘Gonna’ is a common informal way of saying ‘going to’. It’s good for students to recognise well-known slang words but don’t encourage your learners to use them.
In negative sentences you put not after ‘to be’: They are not going to help.