Pokémon Red and Blue/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.

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're playing Blue or Red, and you picked Squirtle or Bulbasaur, you should have an easy time of it, since both of these Pokémon are power against Rock. But if you picked Charmander, you may have a problem... You'll have to level-up your other Pokémon (not Fire, Flying, to Bug, all of which are very weak against Rock) and fight him with those. Alternately, build Charmander up so that it can win the fight through superior strength and HP. A level around 15 to 17 should be sufficient.

Since electric Pikachu is also useless against Rock-types, they made the enemies easier in Yellow. But Yellow can also exploit Rock's other weakness: Fighting! Level 9 Mankeys know the Fighting skill Low Kick and level 12 Nidorans (of either gender) can learn the powerful Double Kick (which they can't learn until level 13 in Red or Blue!)

If you defeat Brock, he'll give you TM 34 (The Bide attack technique) and his Boulder Badge, which grants your Pokémon a small power boost and allows you to use Flash (once you have HM 05).