Your chest produces gold over time, which can be increased with hammers. You can collect your gold by clicking the animated chest in the center, which upon a cooldown timer of one hour must past before you can collect your gold again. Your chest is protected by Heroes you choose as defenders. In the case that your chest is raided, a percentage of gold is protected, and the percentage protected can be increased with hammers. The little green notification gem at the top right corner of My Dungeon indicates that there is gold to be collected.