Instructions:

• Use the tab menu to select a category
• Select a piece and drag to the build area.
• To bring a piece to the very front, just click on it.
• Once you're done, take a screenshot and crop in your image editor.
• What I do is after I crop the image, I use the magic wand tool and click in the area, then I do a Selections/Invert. Copy that and paste as a new image. Save as a transparent png.