But if you're still unsure what Twitter is or why it matters, this post by UNLV j-prof Charlotte-Anne Lucas is a wonderful primer. Much worth reading, including this taste from her intro:
What is Twitter?
It is like a microblog, a place to say your piece, or Tweet, in 140 characters or less.
And it is a place to listen.
Unlike my soapbox of a blog, my Twitter home page is actually a waterfall of other people’s words, blended in a real time river from streams around the world. They are people I have stumbled upon and collected simply by clicking on the button to “follow” them.