The Rock Smash move is a powerful move in the Pokmon FireRed game that allows you to break rocks, which can be useful for progressing through the game. To get Rock Smash, you must first obtain the HM06 item, which is located in the Rusturf Tunnel.
Once you have HM06, you can teach it to one of your Pokmon by speaking to the Move Tutor in the Pokmon Center in Mauville City. The Move Tutor will charge you 1,000 Pokdollars to teach your Pokmon Rock Smash.