During spellcrafting, you will sooner or later stumble across the requirement of Etherium. Etherium is an invisible magical substance that comes in three variants: light, neutral and dark. Each variant is created in its respective generator:
- Neutral -> Obelisk
- Light -> Celestial Prism
- Dark -> Black Aurem
To actually consume the Etherium, you need to link it to the altar by first right-clicking the generator, then the Altar Core with a Crystal Wrench.
To unlink them, select the combination again.
If a spell requires Etherium, the generator is properly linked and has the required Etherium amount of the correct type, simply flip the lever on the altar. The required amount of Etherium will be drawn automatically.