So, what are Fire Kings?
Well, they are a Yu-Gi-Oh! archetype revolving around destruction by card effects. The deck gives you access to plenty of effects that let you destroy cards, and your monsters usually have an effect that triggers when they (or other cards!) are destroyed by card effect.
Because of that, you usually start out by destroying your own Fire King cards in order to get even more cards in rotation, then setting up a board with plenty of effects that destroy both your own cards, and your opponent's. Finally, it all culminates in summoning our boss monster which destroys all monsters on the field.
By carefully sequencing these destruction effects, you generate and maintain card advantage while preventing your opponent from doing so. It's a layered, interactive strategy that is easy to pick up, but certainly rewards skill.
It's also a ton of fun - hopefully, by the end of this guide you'll reach the same conclusion!