Welcome to Pet Talk! To get the "thingy under your name" you need to first resize or crop an image so it is 60 x 60 pixels or less. Then save it to your hard drive, and go to your User CP. Under there hit "edit options" and scroll down, and you'll see where to add your avatar (that's what it's called).

My avatar is Miss Hoppy, she's my little brown bunny! Welcome again!