Fortnite coins?

At the crypt you collect coins like this, do you know what they are for?

There are green XP coins in the game that give you 9000 XP each. There are also golden coins on some creative maps, mostly the team or the player with the most coins wins in the end

Green coins don't tell me anything and I don't gamble in creative mode. I mean the story about zombies, there are tombs as a level where you have to collect coins but what for?

With save the world I don't know myself from sorry.