How to use third-party keyboards on iOS 9?
Apple lets for developers publish third-party keyboards apps in iOS 9.
So Now, you can find huge number of these apps in App Store, and every app have different idea, and it is customize for certain proposal.
To add third-party keyboard, go to App Store and choose app you want, (For example, If you like emoji; install Bitmoji app, while if you use Google Search; install Google Keyboard … etc).
After install Keyboard/s you want, Go to Settings then General, and select (Keyboard) then (Keyboards).
Click on (Add new keyboard) and select keyboard you want (If you have more than keyboard).
Click on new keyboard, and enable (Allow Full Access).
If you want later delete the keyboard, click on (edit) then click on delete icon next to keyboard name.