Then on the left column....look for where it says "Settings and Options"
Under that you will see "Edit Signature". This is where you can add your name, or your tank size, etc. You are allowed to Preview the signature, so you can see if you like it before saving.
To add an avatar (the picture under your nickname), go back to "Settings and Options" in the usercp. Look for "Edit Avatar". Click on that. You can upload a pic from your computer, and size restrictions are listed.