The fire stone is used to evolve certain species of fire Pokemon in Pokemon Pearl, and all Pokemon games. For example, Growlithe and Vulpix require fire stones to reach their evolution state (Arcanine and Ninetaills).
You get a chimchar
You can find a fire stone at Fuego Ironworks, Stark Mountain (With Dowsing Machine).
use a fire stone
Get a Vulpix and use Fire Stone on it!
well eevee evolves into flareon if you use a fire stone on it well eevee evolves into flareon if you use a fire stone on it
You use a fire stone on the vulpix
you have to use an evolution stone like a fire stone, thunderstone etc.
EEVEE GROWLITHE and VULPIX
you can get as many as you want you have to search for it underground of sinnoh
undergruond mineing in walls
Eevee into Flareon, Vulpix into Ninetales and Growlithe into Arcanine.
Well, this may not be helpful, but Fire stones evolve some fire Pokemon... Sun stones also evolve fire Pokemon, (Fire stone, Thunder stone and Water stone also evolve "Eevee", the Pokemon you get after completing sinnoh dex.