The gentlemen from the National Film Society took time out of their otherwise busy schedule to step in front of the video camera and explain the basics of SXSW.
You could read the Wikipedia article on SXSW.
You could visit the official site.
You could follow the #SXSW hashtag on Twitter.
And, you should do all of these things. But, first, you should watch this video from the National Film Society.