Magic Power (not to be confused with Blessing Power) is needed to lift the Binding Spell that is on the dark forested land in your Garden to reveal Cursed Land.
Magic Power can be accumulated by owning Creatures in your Garden as well as owning Mana Pools. Each Creature or Mana Pool gives a certain amount. The higher the level of the creature or pool, the more Magic Power it has.
You can refer to the Creature Book to find out how much Magic Power you currently have.