According to Apple, you can use the emoji keyboard on any iOS device without installing additional applications. In iOS 8.3 and beyond, you can change the skin tone of some emoji characters.
The emoji keyboard became a native feature of iOS with the release of iOS 5 in 2011. To open the emoji keyboard, run any keyboard-enabled application and tap the globe icon located in the lower left portion of your screen. Then, swipe left or swipe right to explore additional emoji icons. If the emoji keyboard does not appear, tap the Settings app, General, Keyboard, and finally the Add New Keyboard. Finally, swipe the emoji keyboard button right to enable the keyboard.