Here's how to get to the Silph Co. Building and defeat Team Rocket:
1. Beat the Gym Leader: First, you need to defeat the Gym Leader in Celadon City, Erika. This will grant you the Cut HM, which you'll need to proceed.
2. Find the entrance: The entrance to the Silph Co. Building is located on a small alleyway next to the Celadon Department Store.
3. Use Cut: Once inside the building, you'll find a tree blocking your path. Use the Cut HM to remove the tree and proceed.
4. Navigate the building: The Silph Co. building is a complex maze. You'll need to solve some puzzles and fight many Team Rocket grunts to reach the top. Be sure to save often!
5. Face the bosses: You'll encounter several key figures in Team Rocket: Giovanni, the leader of the organization, Koga, and Sabrina, the Gym Leader of Saffron City.
6. Save the Pokémon: At the top of the building, you'll find Team Rocket trying to use a rare Pokémon for their evil plans. You'll need to defeat them and stop them.
Good luck!