Blending Fluff is for a soft all over wash of color or to softly blend out a more dramatic application.
For a soft blend or wash, simply pick up shadow to your brush, tap off and sweep all over the entire lid. Finish off with a crème, pencil, or cake liner. 
For use with a more dramatic look, apply all of your color to your lid and crease. Next take your Blending fluff and buff out the whole look without applying any color to the brush. Finish the look with soft highlight, liner, and mascara.