1. Download an emulator, such as VisualBoyAdvance (VBA).
2. Download the ROM of Pokemon LeafGreen.
3. Open VBA and select "Open ROM".
4. Navigate to the folder where you downloaded the Pokemon LeafGreen ROM and select it.
5. Click "Open" and the game will start.
Option 2: Play on an online browser
1. Go to a website that offers online emulation of GBA games, such as MyEmulator.online or RetroGames.cz.
2. Search for Pokemon LeafGreen.
3. Click on the game to start playing.
Note: For both options, you may need to configure the controls before you start playing.