User profiles and pictures / avatars
If you click on "My Account" there is an "Edit" button. Click on that and you can customize your settings.
Most of it is explained on the screen.
If you upload an avatar (picture), the size has to be 85 by 85 pixels. The avatar will show up on any blog or forum posting you make. Currently it will not show up for comments, but maybe I'll enable this for comments.
The other thing to look at is your personal information. At the top of your account edit page is a link marked "Personal Information". That takes you to a page full of questions you might find useful to answer.