By default, under iOS 7, the emoji keyboard, which allows you to enter emoticons in a message for example, is not enabled by default. Follow this tutorial to fix it.
From the home screen, tap on the icon Settings.
Then type successively on General,
and finally Add a keyboard.
Choose to Emoji icons.
The changes are immediate. If you launch the Notes app for example, you will see a new globe-shaped icon. If you type on it, you will then have access to dozens of emoticons to insert into your emails, messages, notes...
An essential option!