Whenever your character begins learning magic, either Celestial or Earth, you must select which of the two is your primary school of magic. The other will be your secondary school, costing more to learn. There is nothing preventing you from learning both Earth and Celestial magic but a separate spell pyramid must be built for each school.
Each school of magic has a Signature Spell—one core piece of magic which is available at every level. For Earth, this is the Cure Wounds / Cause Wounds spell; for Celestial, this is Evocation Bolt. These spells can be memorized in any Spell Slots of the appropriate school that a caster cares to devote to them. Evocation Bolt can be manifested as either Flame, Ice, Lightning, or Stone at the caster’s choice. Cure / Cause Wounds may be cast in either its Earth form as Healing, or its Necromancy form as Chaos. Both choices are made at the time of casting.
When these spells are cast, their power depends on the level of Spell Slot they were memorized in. Each Signature Spell will have a value of 5 per level of Spell Slot it is cast from. For example, a Celestial caster who memorizes one Evocation Bolt at 3rd level will cast it by calling “I Evoke a 15 Flame Bolt!” (or whatever element they chose). If they had one memorized at 5th level as well, they could later cast that one with the call “I Evoke a 25 Ice Bolt!” (or another element). Similarly, an Earth caster could cast a 4th level Cure / Cause Wounds spell as either “I call upon Earth to grant 20 Healing!” or “With Necromancy I create 20 Chaos!”
When these spells are put into scrolls or potions, they must have the appropriate value for the Production Points written on the tag. For example, a Cure Wounds potion created with 5 Production Points (as per a 1st level spell) would be printed as a Healing potion, with the value of 5 written on the tag. Without a value written in, the tag is not valid.