MCCS - new Multiplayer content

Hello everyone, could you please tell me how to use the Elemental Sphere? I put it in my inventory, but nothing happens; it just says "uncharged Elemental Sphere," and so on. I find about 10 of them, but I don't understand how to use them. I've checked the spellbook and the hero's special abilities, but there's nothing there. I've even created 20 heroes, but still nothing.