Mac has come a long way. People now use Mac to communicate through messages (iMessage, Facebook, Jabber etc.). And a prominent part of such personal communication is Emojis. They can spice up a conversation. It's interesting to dramatize your replies (and to express yourself much better) through Emojis. And not to forget, these tiny little icons are really handy when you're not in the mood to type long replies.
You've seen how you can enable Emoji keyboard on your iPhone/iPad. You can also enable the same on your Mac. Unlike iOS, the Emoji menu is contextual so you can access it from anywhere without having to go through a lot of hoops.
How to Type Emoji and other Special Characters on Mac OS X
This works only when the cursor is in a text-field. So make sure you have clicked in an area where you can type (documents, text-fields on webpages, the text-field in Messages app, Notes etc.)
Step #1. Press Command+Control+Space on the keyboard.
Step #2. Emoji menu will pop-up under the cursor.
Step #3. Just click on the emoticon you want to add and you are done.
You'll notice that the Emojis are arranged just the way they're in an iPhone/iPad. You have the recent list followed by the others.
Many of us randomly select emoticons without knowing the exact category they fall in. Here is a short explanation for them: the “smiley” at the bottom of palette refers to People Emojis, the “flower” represents Nature emoticons, the “bell” refers to the Objects Emoji, the “car” shows Places emoticons and the last option displays Symbols.