You start with a stubborn Pikachu, battle the Spearow flock, and meet Misty by stealing her bike.
The free version is fully functional, though the paid version removes ads and adds features like save state synchronization across devices. If you plan to dive deep into the ROM hacking world, the small investment is well worth it.
Use a free Android app like to apply the patch file directly to your clean FireRed ROM.
To find the game files, search online for communities dedicated to ROM hacking.