Iwill & i'm going to : confuse me how to use them?

Mostly we use "will" future as a long time (e.g, I will be ready at ) I'm going to, we use as the things that we want to do right now or after minutes, or
the the difference is the time of action.

When we want to talk about future facts or things we believe to be true about the future, we use 'will'.
The President will serve for four years.

If we are not so certain about the future, we use 'will' with expressions such as 'probably', 'possibly', 'I think', 'I hope'.
example;I hope you'll visit me in my home one day.
If you are making a future prediction based on evidence in the present situation, use 'going to'.
Not a cloud in the sky. It's going to be another warm day.
At the moment of making a decision, use 'will'. Once you have made the decision, talk about it using 'going to'.
example;I'll call Jenny to let her know. Sarah, I need Jenny's number. I'm going to call her about the meeting.