Gold is the most important currency in the kingdom. It can be used to purchase multiple items and bonuses in various menu of the game, as well as to revive troops in the Temple.
You can collect gold on dragon mounds or gold mountains (in case your Kingdom wins the Kingdom clash), accomplish certain achievements in-game or get gold as a bonus from a player who has access to the Royal Treasury. You can win gold by participating in Community events. You can also get gold by claiming daily Free Sales. Finally, you can buy gold in game offers.