to add an avatar

to  i just use the url?

Yes, you do. You add the URL of the image. For example:

http://www.samplesite.com/image.jpg

Look on the toolbar above all of the messages and stuff. Here's what it should say:
Register | Profile |   Private messages | Search | Online  | Help | Create a free blog

Click on "Profile".

Then, in the middle of the new page, it should say:

Edit your profile | E-mail address changing |   Changing/Deleting username | Configure ignore list | AceInfo

Click on "Edit your profile"

Then, about halfway down the new page, it should say "Avatar" with a box to the right. Add the URL in the box.

Finally, click on "Update" on the bottom left corner.

Voila! You have a new avatar!