Gold is the game's primary currency. Check your conquest area. The more zones and demons you have, the larger your conquest area will be, and the more gold that can be collected through taxes.
Training
Spend gold coins on training to maximize your character's performance. Train your characters based on their role. For example, melee tanks such as Death Knight will benefit from absorbing incoming damage. Train them to improve the survival rate. A tank should be placed in the front ranks to protect other characters.