The international date line is needed when you use local times instead of UTC, because the local date is incremented on midnight local time. So, if it's October 19 just after your local midnight, every timezone to the east should also have October 19, while every timezone to the west should still have October 18 because they haven't had local midnight yet. But that doesn't work, since east ultimately meets west when you track both directions far enough. So by convention we have defined a line (or rather a crooked boundary between timezones) where the date jumps back a day in the calendar when you pass over it in an eastwards direction.

Thanks but that much I understand. I guess for people living in that border it doesn’t make sense to me how they can jump back and forth 24 hours.

If I had to live there, I think I would campaign for using UTC only, and forget completely about local time.

The date line itself is in open ocean, so almost no one crosses it on a daily basis.