How do you earn gold?

The way you get gold in this game is by selling things that the monsters drop. Equipment usually sells for more, and if it is good enough of a item you can sell it for a good profit. The best equips are in this order from least to greatest Green/Blue/Purple/Orange. If its only a green gear you will probably just want to sell it to a NPC. You can do this by simply dragging and dropping it to the NPC window that shows all the items you can buy. Umbra/monsters also have their own unique item that they drop. You can sell these too to NPCs for gold.