Treasures are gained from the Treasure Pavilion. To pull in this pavilion requires Merits, you will however get one free pull a day. Merits are gained via Promotion, Regards, and challenges in Office. To use treasures the hero must be level 30.
Treasures have a rarity colour which is the same as heroes and equipment. If you notice a stamp with the word 'Destiny' on the treasure it is to indicate that equipping the item with certain characters will give them an extra stat boost. Keep an eye out for this and equip accordingly when possible to get the boost. You can also enhance treasures with lower level treasures not in use. It is advised that you use blue and green (common) treasures to do this.