Yeah, you have to imagine that you start to fasten before the sun goes on, which starts in Arabian countries even before it starts for example in Europe. So in Paris for instance, you have a delay...
But the first Ramadan-day should be for everyone, which means Friday. So when Ramadan starts in the first country, the people in the other countries should join...
It's a bit complicated, but I hope you understood it a bit... These calculations are even a bit difficult for me. But most people have a calendar, so they can look it up, when they're not sure...or they call at a central to inform themselves (especially the people in Europe ore the US who have more difficulties)