In England we celebrate it to remind us that we were delivered from Catholic tyranny.
A group of religious extremists tried to blow up the King and Parliament so that the Catholics could take over. Guy Fawkes was caught red handed with the barrels of gunpowder in the cellar of Parliament, and the rest of the terrorists were soon rounded up, and later executed.
Britain used to have large bonfires and beacons all over the country to warn of Catholic invasion. Lighting bonfires became they way to celebrate the foiling of the plot.
I think the world over should celebrate it as a way to remember that we will not give into religious extremists who want to impose their religion on us.