The uses of will:
1-Making predictions.
EX:I am sure you will enjoy the film.
EX:I think it will be a good day tomorrow.
2-Making offers and promises.
EX:I will make you a cup of tea.(offer)
EX:I will buy you a computer when you pass the exam.(promise)
3-Certain event in the future.
EX:I will be 30 years next week.
4- Quick decision.
EX: I am hungry.I will eat
The present continuous is used for arrangements.
EX:I am travelling to Liverpool tomorrow.(I have booked a ticket)
The present simple is used for scheduled appointments.(timetable).
EX:The plane leaves at 8 o'clock tomorrow.
EX:The exam finishes at 12 o'clock.
Be going to is used for plans and intentions.
EX:They are going to make a wedding party.(Here they didn't determine.)But if they determine,they use the present continuous.)
It is also used when we predict something based on present evidence.
EX:The sky is full of dark clouds.It is going to rain.