You couldn't avoid hearing about Twitter in 2009, but it has been around since 2006. Twitter describes itself as, “a service for friends, family, and co–workers to communicate and stay connected through the exchange of quick, frequent answers to one simple question: What are you doing?” This short-form messaging tool (140 characters) is new form online communication that is two-way and often used as much as a platform for listening to the communication of others as it is for communicating with others.
If you are a newbie to Twitter and felt left out in 2009, you can find out all you need to know about it before you start using it in 2010 by checking out the free Twitter Guide Book from Mashable.com.
"Twitter is a social network used by millions of people, and thousands more are signing up every day to send short messages to groups of friends. But where's the user manual for Twitter? Where do new Twitter users go to learn about Tweeting, retweets, hashtags and customizing your Twitter profile? Where do you go if you want to know all about building a community on Twitter, or using Twitter for business? How can you find advanced tools for using Twitter on your phone or your desktop? To answer all these questions and more, we've assembled The Twitter Guide Book, a complete collection of resources for mastering Twitter." - Pete Cashmore, @Mashable