G Cloud can backup your apps data (your games data, levels, whatsapp messages …etc), but not the apps themselves.To backup your apps data, you’ll need to:
1. Purchase G Cloud Apps Backup Key ★ root which provides this feature (Backup the apps data).
2. Root your phone: This app (G Cloud Apps Backup Key ★ root) needs root access in order to backup apps data.
Root access means hacking your phone to get super privileges. If you have never done this, then the app will not backup your apps.
For more about Android rooting, please refer to the following article: