Inserting emoji, the Japanese emoticons, is easy in apps like Whatsapp. It has a special icon for Emoji to the left of the message box which can be used to insert these emoticons. The stock Android keyboard does have Emoji support, but it is hidden away and is not displayed most of the times.
Emoji can be inserted in any app while typing any text using the default Android keyboard. Just press and hold the
Send key. A smiley face appears. Without releasing your finger press, move to the smiley face and release your finger. You get the emoji keyboard now, where you can choose whatever emoticon you want to insert.
Tried with: Android 4.4.4 and Moto G