If you are using the latest iOS - you already have all the possible emoji on your keyboard.
If you do not have the emoji keyboard enabled, please go to Settings > General > Keyboard > Keyboards > Add New Keyboard > Emoji. (See How to enable Emoji keyboard.) After that you can always get access to Emoji keyboard by tapping on the "globe" button.
However, some people find the standard keyboard not really convenient, and that's exactly were our app can help you.