Installation and activation
Once the app is installed, go to the main menu, open the system Settings app, and select General > Keyboard > Keyboards > Add New Keyboard.... That will show the list of installed keyboards, which contains a separate section with the custom (third-party) ones. Once you've tapped on the row labeled StoneKey, the keyboard is ready for use.
Activating StoneKey keyboardTo start using the StoneKey keyboard, press and hold the key with the Globe symbol until the list of available keyboards appears, and slide to the item labeled StoneKey — StoneKey. Alternatively, tap the Globe key several times until the desired keyboard finally appears.