Okay to set up your avatar all you need to do is:
On the top of your screen is a button that says 'Profile' click on it and that takes you to a page that has all of your details and you will see a link that says 'Avatar' click on it and then just click 'browse' which allows you to upload an image off of your computer onto the internet to be used as your avatar.
WARNING YOUR AVATAR MUST BE 100x100 PIXELS BIG!
I WILL NOT TOLERATE ANY BIGGER IMAGES!!!!
ANY BIGGER AND I WILL RESIZE YOUR IMAGE AND I MIGHT GIVE YOU A TEMPOARY BAN!!!! (yes I am allowed to and I am this strick when it comes to things like this)