GOING TO (FUTURE PLANS)

We use going to talk about future plans or intentions.
Besides we use expressions that accompany going to how:
Tonight, next week, this afternoon, etc.

Pronoun+ verb to be + going to + main verb
I am going to study Affirmative form

We form the future with going to:
Pronoun + verb be + Going to + main verb
I am going to study

Pronoun + verb Be + not + Going to + main verb
I am not going to sleep Negative form.

Verb to be + pronoun + Going to + main verb.
Are you going to eat salad? Interrogative form

In this case you can use the short answer as:
Yes, I am/ No, I´m not

Or composed answer as:
I don´t know. I´m going to chose another thing

Informal contractions are short forms of other words that people use when speaking casually. "gonna" is a short form of "going to". For example:
What are you gonna do tonight?
I'm gonna stay home.

Where are you gonna eat?
I´m gonna at the restaurant
When are you gonna to travel?
I ´m gonna in Saturday.

http://www.sherton.com.ar/goingwill/going.htm
http://www.better-english.com/grammar/goingto4.htm