How is that done?
From where you are right now:
Top row, click on "Profile".
That will take you to your profile screen.
On left side of screen, you'll see a heading labeled "Modify Profile", and under that, "Forum Profile Information". Click on the second link.
On that page, you can upload avatar, make a quote for underneath, a "signature" which will appear under each of your posts, and other information. When you're done, click on the "Change Profile" button on the bottom of the page to keep the changes.