What’s an Avatar? The sweet little picture you see next to my name when I comment now.
How do I get one? Go to www.gravatar.com, and register using whatever e-mail address you registered here.
What if I don’t want one? You can change the settings easily. Scroll down the page to the “Meta” box, there should be a tools/settings link. Make sure you’re logged in, and go under Settings -> Discussion, scroll down, and select “no avatar” or something like that.