Helpful tips to understand 

The difference between going to future and will

Have a look at what I´ve found at 7ESL.com

Will and Going to Similarity in Usage

• Both Will and Going to can be used for making future predictions without having a real difference in meaning.

Example:

I think it will be foggy tomorrow. = I think it is going to be foggy tomorrow.

Will and Going to Differences in Usage

• Will is used to express future actions decided at the moment of speaking while Going to describes future plans decided before the moment of speaking.

Examples:

I‘ll have salad now. (will)

I’m going to visit my aunt next Friday. (going to)

• Will is used to indicate a prediction based on personal opinions or experiences while going to is used to express a prediction based on present evidence.

Examples:

I think United will win the game. (will)

Look at those black clouds. It is going to rain. (going to)

• Will expresses a future fact; going to is used to describe something is about to happen.

Examples:

The sun will rise tomorrow. (will)

Get back! The bomb is going to explode. (going to)

• Will is used to make a promise, an offer, a threat or refusal.

Examples:

A promise:

I promise I won’t tell anyone you broke the window.

An offer:

I‘ll take you to the airport tomorrow.

A threat:

I‘ll tell your parents what you did.

A refusal:

No, I won’t cook your dinner, you can cook it yourself.