-Do you mean you want to upload a pic? Well, if thats what you want to do, look at the top of your screen. There should be a bar. One of the icons is labled "Gallery". Click on the icon and click upload pictures. Click on the browse button, and select the screenshot you would like to upload. It may take some time for your pic to be approved, but don't worry, as long as it meets TTC's guidelines, it will be accepted.
-If you would like to view the TONS of free avatars TTC offers, click on "User CP" (Its on the same bar as gallery) Once in UserCP, look to the left. Click on "Edit Avatar" You will have the choice to upload an avatar from your machine or select one of the ones TTC offers. You can browse through the great avatar selection.
-Now if this doesn't answer your question couldya be more specific as to what you want to do?
Hope it helps

~PCPF