You set up an Avatar in the same way you do in any phpBB powered board.
Yiu shouls consider that as per the configuration, you must upload a small image with a max. of 10Kb (I think).
If you want to do this you have to browse for your avatar in the field with the tag "Carregar o Avatar a partir do seu computador:"
If you want to have an avatar in any picture server you have to place the url in the next box (tag "Carregar o Avatar a partir de um URL:")
Hope this helps.