Avatars are those are the little pictures under your screen name alongside your posts, like my cool butterfly here.
To add/change your avatar, click on the Member Center button near the top of the screen, then the Avatar Settings link on the left. There are lots of places on the web that offer free avatars, just google it. Or you can use one of your own photos, cropped and/or resized as needed.
Tip: If you don't want your avatar streeeetched and distorted, make sure the numbers for the avatar dimensions are the same ratio as the actual picture dimensions. Example 1: If your actual picture is 100x85, make your avatar dimensions the same. Example 2: If your actual picture is 300x150, make your avatar dimensions 100x50 (that is, the same 2:1 ratio of height to width). Generally right-clicking on a picture and looking at its properties will tell you its dimensions.