PNG avatars:

Create a layer, delete any other layer that is not transparent. Add text, and a design (such as a swirl) if desired. To add an image, take your desire image, open it in a separate layer. Select the text or design you would like have the image then invert it. Press delete/cut to delete the area around the text/design. Now the image should be cut in the shape of the text or design. :) Make sure to export as PNG otherwise the background won't be transparent.