future plans an intentions

use going to NOT will won't when you have already decided to do something.With the verb go you can leave out the infinivite.


future arrangements

you can usually use present continuous or going to for future plans arrangements.
going to shows that you have ma a decision
we are going to get married in the summer
present continuous emphasizes that you have made the arragements.

we are getting married on July 12 th


use will won't ( NOT the present simple) for instant decisions,promises,offers,and suggestions

Use will or going to for predictions.