Gold is the primary currency in Curse of Aros. It can be obtained by fighting monsters.
You obtain gold by killing monsters and selling items to the Merchant. Every mob drops gold, but they also drop equipment - and once you start collecting duplicates be sure to sell them off for a little extra in your pocket!
As of right now, the best place to farm for gold is the Ice Spiders. Their respawn rate is quick, and they drop a multitude of equipment that you can sell for a quick profit. At lower levels, focus on the Forest Spiders until you gain enough strength to face higher level monsters.