Facebook is expanding the use of emoticons on the site. If this was any other site, no one would care, but seeing as Facebook is used by one billion people every month and that communication is still the main purpose of the site, it's a move that affects a lot of people.
Graphical emoticons were already used in Facebook chat, but characters remained characters everywhere on the site. Not anymore, news feed comments now convert emoticons into graphical representations.
Emoticons are still not used in the news feed posts or everywhere else, just in the comments for now. There's no way to insert them, they're converted after you post the comment.
Facebook also recently added emoticons to its mobile Facebook Messenger app, but the graphics are different. Facebook may expand the use of emoticons, but may not add them to posts or at least, it won't add a menu entry to insert emoticons when posting something.