Upon reaching Viridian City, you'll find an old man blocking the path north. Head into the Pokémon Mart to receive Oak's Parcel. Return to Pallet Town to deliver it to Professor Oak. In return, he'll give you the Pokédex, a device to record all the Pokémon you encounter, and five Poké Balls to start your catching journey. Now you can head back to Viridian City and proceed north.
