After exiting the Viridian Forest and taking a short walk northward, you will find yourself in Pewter City, which hosts the first gym. But, before going to the gym, it might be smart to walk around, talk to people, and break into random people's houses. Trying to go to the next route will cause an annoying kid to force you to go to the local gym. You can also pay 50 Poké Dollars to go into the museum and look around, but this place is useless... for now.
Go to the Brock RBY page for details about the Red, Blue and Yellow Pewter Gym leader, Brock.
Go to the Brock FRLG page for details about the FireRed and LeafGreen Pewter Gym's leader, Brock.
Pewter City continuedEdit
After you curbstomp Brock and get the Boulder Badge, you can start to make you way to the east and see the hilarity that is Route 3. After getting HM01 Cut, you can go back to Pewter City and cut down the bush next to the museum, which will give you access to the staff-only door. Out of respect of your complete disregard for rules, the man at the counter will give you the Old Amber, which you can resurrect into an Aerodactyl in the laboratory on Cinnabar Island. One of the other scientists is willing to teach one your Pokémon Seismic Toss in FireRed and LeafGreen. Pewter City is no longer of any use after this other than as a place to Fly to.