The Future: (to) be going to

The present continuous form referred to future actions (I am going to/we are planning to), means that I/We have already decided and arranged to do something.

situation example:

- What are you doing for Christmas Holidays?
- I think, we are going to ski in Slovakia on the Low Tatras.
- That's awesome! How many of you are planning to go?
- We are six in total, we are managing to rent a bungalow not far from the slopes.
- I wish you to have fun guys!!

• Present continuous can be also used just before we begin to do something. example:  

      -  She is going to give up smoking.
      -  If I look at the clouds, I deduct is going to snow, before evening. 

• To talk about something refereed to the past, it is used the form I was going to= I intended to do it, but I didn't do it:

     - I was going to call you, but Sue stopped me in the shop and I forgot.
      - It looked like it was going to snow, but in the end it didn't.

Tips:

Informal contractions are short forms of other words that people use when speaking casually: they are a little like slang.

For example, "gonna" is a short form of "going to".

If you say "going to" very fast, without carefully pronouncing each word, it can sound like "gonna".

Please remember that these are informal contractions: that means that in formal written English are not used, neither in writing.
They are normally used only when speaking fast and casually, for example with friends.
It is probably true to say that informal contractions are more common in American English.