Pokémon Gold and Silver/Pewter City

'In Pewter City, you will fight Brock, your first Pokémon Gym Leader. The Pokémon he uses in battle are strong. If necessary, build up the experience of your own Pokémon by having battles in the wild. Before you do either, visit the Pokémon Center in Pewter City, so if your Pokémon faint in battle, you'll resume your journey there, instead of far away.'

You can't leave
If you try to leave town to the East, you'll be sent to deal with the town's trainer, Brock, at the Gym in the middle of town, below the Museum. Until you've bested him, you're stuck here. While you're in town, in Silver Version go into the top right portion of town and talk to an old man with blue hair. He will give you Rainbow Wing, which you can later use to capture Ho-oh in the Tin Tower back in Johto. In Crystal Version an old man facing the route pointing east will give you Silver Wing, which can be used to capture Lugia at Whirl Islands. In Gold Version, there is a man standing next to the Mart who will give you SILVER WING which is necessary for capturing Lugia.

The Science Museum
It'll cost ya 50 to get into the Museum (the large building in the North part of town), and while there's lots of interesting exhibits, nothing here will help you directly. The good stuff is in the back, but that way is blocked by one of those annoying plants... You'll have to come back later.

Here's a silly trick for the Yellow version: What the father upstairs says changes based on your Pikachu's mood. If your Pikachu is clearly upset (if you've left him in the computer too long, for example), he'll ask you to give him to his daughter! But the game won't actually let you.

Trainer Battle 1: BROCK
Both Brock and his Junior Trainer use Rock-type Pokémon, and your only chance at victory is to face Brock and his minion with Grass, Water, or Fighting-type Pokémon of your own.

If you defeat Brock, he'll give you the Boulder Badge, which grants your Pokémon a small power boost.