After you battle your friend in Route 203, you continue east and reach Oreburgh Gate on your way to Oreburgh City.
Get TMs and a Pokétch App
Go east and you will receive some TM98s. They can teach Rock Smash to a pokémon. Each one can only be used once.
You will also get the Hidden Moves app added to your Pokétch. It lets you use Hidden Moves, such as Rock Smash, in the field, but you won't be able to do so until you get the Gym Badge from Oreburgh City.
In the cave, you can catch Geodude and Zubat.
Go east and you can battle Camper Curtis. He has a level 7 Shinx. You get 392 Pokédollars for winning.
Go east and you can battle Picnicker Diana. She has a level 5 Budew and a level 5 Psyduck. You get 380 Pokédollars for winning.
Go east from there to reach Oreburgh City.