Smileys a unique to express your feelings which we used to add to facebook using 3rd party services like facemoods or using other smileys trick but well now you do not need any extra service or other stuff as Facebook as released their smileys and embed them directly into the chat like in the image on the right.
You just have to visit your facebook profile and click on any friend with whom you wanna chat, now right in the text box you will see the smiley icon which when clicked will popup the smileys which you can click on add in your chat.
They have also included the like button which can be used if your friend asks that how he is looking or any other liking questions pretty cool.
Benefits of using the official smileys is that you do not need to install or add any plugin to use the smileys, these are official ones and maybe more will be added in the future. so have fun chatting with your friends and sending some gracious smileys :)