The Fire Spell is one of the Magic scrolls, and learned by using the Fire Spell Scroll, which may be looted from the Fire Snake in the Volcano.
The Fire Spell requires the player to have 1 magic bonus, which you can get from equipping the Wooden Staff (and Reaper armour later on), that is why Combat Presets are suggested to use. The spell itself costs 3 Mana 
and deals 0 - 5 damage (double damage to all enemies within the Northern Fields).
The Fire Spell has a cooldown of 6 seconds.
The Fire Spell will also be required for Combat Presets and Shiny Resources Quests.