What is the immediate future tense and why is it different to the future tense?

The immediate future tense translates as 'going to...'. It describes an action that is about to take place in the near future, so you can use it for events likely to happen soon/immediately. By contrast, the future tense translates as 'will...' and tends to suggest a pause between saying it and the action actually happening. The event could happen at any time in the future - maybe even 100 years away!