From The Walkscape Walkthrough

Coins are the currency of WalkScape. You can get coins by selling items to a shop or as a drop from a chest. Chests have a 21.64% chance of dropping between 10-100 money per loot roll (4 rolls per chest).

Currently the uses for coins are quite limited (with one notable exception). Coins are generally used to purchase materials or equipment from the various shops across Arenum. However, to travel outside of the starting area of Jarvonia, a player is required to purchase a Jarvonian Letter of Passage. This special collectible item costs 4.5K coins and grants the player further access to the world map through the GDTE.

Once player-to-player trading is added, coins will play a more important role as it will be essential for the player based economy to function.