"Will" often suggests that a speaker will do something voluntarily. A voluntary action is one the speaker offers to do for someone else.
USE 2 "WILL" to express a promise
"Will is usually used in promises
EXAMPLE: I will call when I arrived
FORM BE GOING TO
(BE+GOING TO+VERB)
EXAMPLE:You are going to meet Jane tonight.
USE 1 "BE GOING TO" To express a plan
BE GOING TO: expresses that something is a plan. it expressed the idea that a person intends to do something in the future.
EXAMPLE: He is going to spend his vacation in Acapulco
USE "WILL" OR "BE GOING TO" TO EXPRESS A PREDICTION
Both "will" and "be going to" can express the idea of a general prediction about the future. Predictions are guesses about what might happen in the future.