The Ener Zone (エナゾーン Ena Zōn) is the Zone to the left of all of the other Zones. The cards in it are used to pay ener costs; to pay an ener cost, put the requisite type and number of cards from the Ener Zone into the trash.
During the ener phase of your turn, after upping all of your cards and drawing your cards, you may put a card in your hand OR one SIGNI on your field on the field into the Ener Zone; this action is called ener charging. SIGNI go to the Ener Zone after being vanished, and Life Cloth are put into the Ener Zone from the Check Zone after being crushed.