To get the Rock Smash HM in Pokémon Emerald, follow these steps:

1. Head to Mauville City: This is the city where you will find the Rock Smash HM.

2. Locate the House: The house where you can obtain Rock Smash is located to the right of the Poké Mart in Mauville City. It is situated in the lower-right corner of the city, just adjacent to the Poké Mart.

3. Enter the House: Inside this house, you will find a man sitting at a table.

4. Talk to the Man: Speak to the man at the table. He will give you HM06, which is Rock Smash, if you have the Stone Badge and the Knuckle Badge.

5. Teach a Pokémon Rock Smash: Once you have obtained HM06, you can teach it to any of your Pokémon by selecting the HM from your Pokémon menu and choosing the Pokémon you want to learn it from.

Additional Information
– Dynamo Badge Requirement: You need to have the Dynamo Badge to use Rock Smash outside of battle. This badge is obtained after beating Wattson in the Mauville City Gym.
– Using Rock Smash: Rock Smash is used to break rocks, which can sometimes yield specific Pokémon like Nosepass or Shuckle.

By following these steps, you will be able to obtain and use Rock Smash in Pokémon Emerald.