An avatar is the picture that is displayed next to you username.   This is how you add an avatar to your username

Click the "profile" botton at the top of the page.

On the left you will see a link that says "forum profile information" Click on this address

You now have two options:
The first is "I have my own pic".     If you click the button you need to have a picture on host site.   Add the link to the host site the picture is at and hit "change profile" on the bottom of the page.

The second option is " I will upload my own picture".  You can click the botton and find your own picture that is on your computer by clicking the browse button and finding it.    When you have clicked the directory to the picture in the box you can now hit the "change profile" button and you are all set.   Have fun!