To add an image to use as your avatar (a small picture shown under your user name), click on the "Profile" text at the top of the page.

When your profile page loads, scroll to the bottom and click the "browse" button next to the text "Upload Avatar from your machine". You will then be prompted to find the picture you want to use on your local drive, after you have located it, click the "Open" button.

Now all you have to do is click the "Submit" button at the bottom of your profile page.

Your Avatar picture must be 120x120 pixels or smaller and be less than 6K in size.