Pokémon FireRed and LeafGreen/Celadon City

Celadon City is the largest city in this game. Its PokeMart has six stories; no wonder it needs an elevator! They sell all sorts of things. You'll be able to buy TMs and normal items (such as Potion and Antidotes) on the second floor. On the third floor, you'll see many people playing Game Boy Advances. Talk to the person at the register, a Move Tutor, and he'll teach one of your Pokémon the move Counter. The fourth floor has many evolution stones you can buy to evolve certain of Pokémon (ex. Eevee) for $2100 each. On the fifth floor, you'll be able to buy items such as X Attack and Calcium. These are items that modify a Pokémon's stats so they can do better in battle. Finally, you'll reach the rooftop, where you'll find three vending machines and two people, including a little girl. Get a Fresh Water, a Soda Pop, and a Lemonade from the vending machine, and give it to the little girl one at a time. She'll give you TM16 - Light Screen, TM20 - Safeguard, and TM33 - Reflect, respectively, for your drinks.

Celadon Mansion
There is a huge building to the right of the department store that's nearly empty inside. Talk to the old lady who's surrounded by Pokémon on the first floor. She'll give you Tea, which you can give to any one of the Saffron City guards so they can let you through. You'll also find the game's programmers in this building, one of which will tell you to return after getting all the Pokémon. He'll give you a diploma for catching all the Pokémon.

Now leave the mansion, and go in through the back door. Go all the way to the rooftop, where you'll find a small building. Inside you'll find a person and a PokeBall on the table. Pick it up; it's an Eevee!

Other Stuff
The restaurant south of the Game Corner has a man who'll give you a Coin Case to carry your coins. There is an old man to the left of the Game Corner, and can be reached only by surfing across the water. He's a Move Tutor, and can teach your Pokémon Softboiled.

Game Corner
Now go to the Game Corner, a place full of slot machines and people on them. Team Rocket made it, and you win or buy coins in order to trade it in for Pokémon and TMs in the building to the right of the Game Corner. A few people will give you free coins, and there are invisible coins scattered on the ground that you can pick up. At the top of the Game Corner, battle the Rocket member, and push the button on the poster. A staircase leading to the basement appears.

Team Rocket's Hideout
After that, you'll be going through four floors, battling Rocket members and collecting valuble items. There is a spin maze on the second basement floor (B2F). The arrows in the maze will toss you in whichever direction the arrow points. Here, you'll pick up a few items including a Moon Stone and TM12 - Taunt. On B3F, you'll find TM21 - Frustration and Blackglasses, which boosts the power of Dark Pokémon. There is another spin maze on this floor where you can pick up a Rare Candy. Head to B4F, where you'll find TM49 - Snatch. Battle the single Rocket member at the top, and he'll drop the Lift Key for the elevator. Take the elevator on B2F to B1F. Battle the Rocket member, and take the elevator again to B4F. Go all the way to the left, and pick up the Calcium. Head up to the two Rocket guards and talk to them. They'll fight you, and after you're through with them, they'll open the gates.

The Boss
Walk through the entrance, and you'll face Giovanni, the head of Team Rocket, in an intense match. He has a lv. 25 Onix, a lv. 24 Rhyhorn, and a lv. 29 Kangaskhan. A Grass or Water-type Pokémon would work out fine fighting this guy. However, beware of his Kangaskhan, as it can be very powerful. After beating Giovanni, he'll disappear, and leave behind a Silph Scope. This is used to detect Ghost Pokémon.

Gym Battle
After beating Giovanni in the Game Corner, head to the gym by cutting the tree. Here you will battle Erika and other trainers. Erika is the trainer in the middle between the two trainers inside the enclosed area. Beating her earns you TM19 - Giga Drain and the Rainbow Badge!