The technique involves fusing two fabrics together (in the above piece- the green background and the orange and in the photo below- the green background and the red), then using the tool to cut angled slots which make the triangles which you then turn out to leave empty space below. That space is filled with backing fabric (purple above and the yellow below). Instructions and an entire gallery of ideas for how to use the Double Diamond Ruler can be found at Kim's Website and this link: How to Instructions.
This piece, which I call "Christmas Tree" Quilt #8769 is for sale at the Alzheimer's Art Quilt Initiative Website (AAQI) under my $1000 Promise page.
Profits from the sale of all AAQI donated quilts go to fund Alzheimer's research projects. Since January 2006, the Alzheimer's Art Quilt Initiative has raised over $704,000 for Alzheimer's research. The projects funded by the sale of these small quilts (all 9 by 12 inches or smaller) are detailed under the Research Tab on the AAQI Website.