To get an avatar, click on "GO" in the upper left portion of the tool bar. From there, click on 'My space" and then "Profile." When your profile comes up, in the upper right hand corner, there is a link to "View/Edit" your profile. Click on that.
When that page comes up, scroll down to the "Public Profile Fields," and you'll see "Avatar/Picture URL." Click on "edit" on that line, and you can choose from a bunch of avatars.
Once you save the avatar you've chosen, yours will appear with your name when you post.
Have fun choosing an avatar!!