You use will and to be going to when something is going to happen in the future
Af.: Are you hungry? I will get you something to eat.
Af.: Look at those clouds! It is going to rain in a minute.
Neg.: I won´t (will not) help you, you can do it yourself.
Neg.: I am not going to the party next Saturday.
Question: Will you make me something to eat?
Question: Are we going to watch Harry Potter?
Will/shall, to be going to ± infinitive