if the decision to act was made before the time of speaking, ‘going to’ must be used; if not, ‘will’ must be used. I'm going to go on holiday next week. I'll get it!

Hello Akhra! I know you already received answers, but they are not accurate. There is a considerable difference between the two forms. "Going to" is used with plan, things that have been programmed or scheduled, things that you intend to do. With the verbs of motion, you just use the gerund of that verb: I'm going, flying, traveling, etc. : We're going to China this summer. What cities are you going to visit? Otherwise, it expresses a confirmed decision to do something: I'm going to tell Dad what you said. We're going to buy a new car. I'm going to look for another job - I hate this one. Rita is going to learn Russian. In the above examples, you can't use "will." It would make no sense, because it wouldn't let the listener know that these are concrete decisions or scheduled trips, etc. "Will" is used when you are offering to do something, proposing something. For example, if your sister tells you that her car broke down, you can say: "I'll pick your children up from school." This is not a concrete plan, because your sister may have other plans - you are simply offering the future possibility of picking up the kids. You're proposing a solution. Sister: My car broke down. You: I'll pick the kids up - what time? Sister: Three. (later that day, your friend calls) Friend: Hey, do you want to go fishing? You: I can't - I'm picking my sister's kids up at three. Note the difference in "will pick up the kids" and "I'm picking up my sister's kids." (you can use the gerund here, because picking them up involves driving - a form of motion verb). I hope this helps. Let me know if you have any questions.

To 99% of English speakers, 'will' and 'to be going to' are exactly the same. There isn't even a technical difference - people tend to use 'going to' slightly more often when a decision has already been made just out of habit, and so when people who know the technicalities of English (such as on this website) are asked the difference between the two words, they describe that small difference. If you keep thinking they mean different things, then you'll get very confused when you hear native speakers use the two interchangeably. I think in general "going to" tends to be used more often, but that's about it.