How does twitter work?

[Betabite]

I'm trying it out and I don't get it. What am I supposed to do on there?

[dan]

Twitter is a social networking and microblogging service that enables its users to send and read other user messages called tweets. Tweets are text-based posts of up to 140 characters displayed on the author's profile page. Tweets are publicly visible by default, however senders can restrict message delivery to their friends list. Users may subscribe to other author tweets — this is known as following and subscribers are known as followers.