An APK (Android Package Kit) is the installer file. Think of it as the "setup.exe" for Android. It contains the code, resources, and manifest for the app. For a game like GTA 5, the APK is tiny—usually 50MB to 100MB. It tells your phone how to launch the game, but it contains almost zero game data.
Playing GTA 5 on Android: Official Status and Safe Alternatives Grand Theft Auto V (GTA 5) Gta 5 Apk And Obb File Download For Android
The OBB (Opaque Binary Blob) file is where the magic lives. This is the data file containing graphics, textures, audio, maps, and missions. For high-end games like GTA: San Andreas, the OBB file is around 2.5GB. An APK (Android Package Kit) is the installer file