There are several types of emoticons. Some require keyboard combinations, such as a colon and parenthesis for a smile, but others are site specific and convert into different faces depending on what is typed.
There are three major types of emoticons. The first and most simple are those that combine parentheses or slashes with colons. These can be used to form smiley faces and frowning faces or even indifferent faces. On some sites, such as Facebook, entering these keystrokes makes an animated face.
The second type of emoticon uses both parentheticals and the aforementioned keystrokes to make fuller faces. It may also use letters, such as in XD or :D, to make more exuberant faces. These sometimes translate to forums and Facebook as particular faces, but not always.
The third type of emoticon is the Japanese style emoticon. These often require keystrokes that are unique to keyboards with Japanese language equipped. An alternative is to copy and paste them from a Japanese emoticon website.
Mobile devices, such as smartphones and tablets, often have emoticon tables available for sites like Facebook and Twitter, and the user only need select them and go. Emoticons and meanings change constantly, similar to how Internet slang is often fueled by teenagers.