After you obtain your starter Pokémon, Professor Birch asks you to meet with his child in Route 103, but before you can get there, you have to go through Route 101.

Go Through the Route

To get through the route, go north, then east through some grass. If you are attacked, just attack until the pokémon is defeated, or you can try to run away. You can go back to your house and talk to Mom if your pokémon is low on health.

Otherwise, after going through the first area of grass, go north through the next area of grass. Then go north to the exit. You will reach Oldale Town.