future with will - use
We use the simple future for:
1. A decision at the moment of speaking (a spontaneous action):
I'm cold.
I'll close the window.
2. Prediction based on opinion:
I think the Conservatives will win the next election.
3. A future fact:
The sun will rise at 7am.
4. Promises / requests / refusal / willingness:
I'll help you with your homework.
Will you give me a hand?
I will give up smoking!
Shall is used mainly in the forms shall I? and shall we? in British English.
These forms are used when you want to get someone's opinion, especially for offers and suggestions:
We use be going to + infinitive for:
1. Future plans made before the moment of speaking:
We've run out of milk.
I know, I'm going to buy some.
2. Prediction based on present evidence:
Look at those boys playing football! They're going to break the window.