After you rescue Professor Birch from the wild pokémon, he tells you to go to Route 103 to meet his child. You go through Oldale Town on the way.
Receive a Gift
As soon as you enter Oldale Town, a shopkeeper comes up to you and tells you about the Poké Mart, which has a blue roof. The shopkeeper then gives you ten potions. After that, he shows you the Pokémon Center, which has a red roof. You can go there to heal your pokémon for free.
Continue to the Next Route
The Poké Mart in Oldale Town is sold out of poké balls, and they are only selling potions right now, so you should move on to the next route.
You can't go west from Oldale Town because someone wants to sketch the rare pokémon footprints there, so go north and you will reach Route 103.