Gold is earned both passively and earned by defeating monsters in the jungle, last-hitting wave minions (which is shared among nearby allies), killing enemy players, and completing Quests.
This amount can be increased to 600 with the Traveling Chest Hero Gear.
Passive Gold Income:
This amount can be increased to 1.8 /sec with the Traveling Chest Hero Gear.
When you have the Gilded Lantern Hero Gear equipped, wards you place grant you a stacking bonus to Passive Gold Income and enemy wards you destroy are worth additional gold.
You can increase your Gold income per second by buying any of these items:
Merchant's Ledger +0.6 /sec
Merchant's Vest +0.6 /sec
Merchant's Wine Skin +0.6 /sec
Scrying Mirror +0.6 /sec
A unique feature in Sins of a Dark Age is the Shared Gold Mechanic, which allows for nearby teammates to earn gold even when they aren't the last hitter. The last hitter always receives the full value but any nearby ally heroes will split a separate pool. This change allows for more gold income for Support heroes and less team in-fighting over last hit gold.
In the screenshot below, the Vexie player is getting the last hit and getting 25 Gold.
However in this screenshot, a nearby Beroth ally is getting the last hit on the minion, but Vexie is still getting Gold because of the Shared Gold Mechanic.
Learn more about unique features in Sins of a Dark Age by going to What Makes Sins of a Dark Age Unique?