Spell casters are often referred to as Essence Weavers.
Magic comes in many forms, shapes and sizes. Some examples follow.
Essence Points are special Fate Points that can be stored, but may only be spent when casting magic. Unlike fate Points you can spend as many Essence Points you want on a single aspect, their effects all stacking together.
Essence is also the magical fuel that the Star beast require for nourishment.
Iron acts to nullify the effects and power of Essence and therefore the presence of iron often interferes with magic.
Lengthy and involved rituals may provide additional EPs for the purpose of casting certain spells. If you need more EP to create the effect you want, simply declare that you want to cast the Magic effect as a Ritual. The GM will tell you what you need (ingredients, special location, participants, etc) and how long it will take. You may need to pass a Challenge (multiple skill rolls) to meet the requirements of Ritual Magic.
Essence gathers in certain magical locations all over the universe. Particularly at sites of significance – groves, temples, and areas of great natural beauty. The Essence of these locations can be harvested, usually through ritual, being there at a certain time of day, or through some other process; occasionally some form of sacrifice.
Every being has deep hidden connections with the Essence around them. Objects that someone has possessed for a long time, or are otherwise of a personal natural, contain the Essence imprint of their owner. These objects can be used in magic and ritual to create a magical connection to their owner.