<I'm going to + VERB> is one example of the many structures we have in English to describe the future, Bieasy. But it isn't a 'tense'.
English doesn't really have a future tense because, as I mentioned above, there are numerous structures used to describe the future.
be going to / will / be about to / present simple / present continuous for the future / should / would / can / could / might / may / shall / want to / have to / must / plan to / ...
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