Summarize the following:
Tap the Settings app icon, which resembles a grey box with gears on it. This option is near the top of the Settings page. It's near the bottom of the "General" page. You'll find this near the top of the screen. Doing so opens a list of keyboards that you currently have active on your iPhone. If you see an option labeled Emoji in the list of keyboards near the top of the screen, your iPhone's emoji keyboard is already enabled and you can proceed to using the keyboard. If not, proceed. It's near the middle of the screen. This will bring up a list of available keyboards. You'll find it in the "E" section of the keyboards page. Tapping it will immediately add it to your iPhone's keyboard. Press the Home button at the bottom of your iPhone's screen to do so. You can now use emoji from your iPhone's keyboard.

Summary:
Open your iPhone's Settings . Scroll down and tap  General. Scroll down and tap Keyboard. Tap Keyboards. Look for the Emoji keyboard here. Tap Add New Keyboard…. Scroll down and tap Emoji. Close the Settings app.