You can Special Summon this card (from your hand) by banishing 1 LIGHT Dragon-Type monster and 1 Dragon-Type Normal Monster from your Graveyard. If this face-up card on the field would be destroyed, you can Tribute 1 face-up "Hieratic" monster instead, except this card.
Hieratic Seal from the Ashes is a great way to to setup your graveyard by sending Hieratic Seal of the Sun Dragon Overlord and Hieratic Seal of the Dragon King to the graveyard. Additionally, it returns your removed from play Hieratic monsters to the graveyard. Hieratic Supremacy simply special summons any Hieratic monster from your hand.