Pebbles are a currency of the Cyan Plex Server, which you could use in the Pebble Merchant.
Buy Pebbles to support the server! Pebbles are used to buy different things on the Pebble shop. To access the shop, use the npc at the spawn. You could buy tags, flight times and more with your Pebbles!
Pebbles could be earned without buying them. By completing quest and fulfilling playtime level requirement you can earn pebbles.