This has several uses, all of which help the photographer manipulate the lighting in a photograph. The reflective surfaces are designed to bounce light from the sun or other light source onto the subject, in order to fill shadows or enhance the lighting. The gold reflective surface will "shower" the subject with flecks of warm-toned light (think of it as a soft mirror that you might use to redirect the sun into your subject's face). The silver surface will do the same, but with a neutral-toned light. The solid white surface will reflect soft light without the added flecks or highlights (great for filling shadows on a subject's face). There is also a rigid, translucent, white panel that you could place between the light source (i.e. the sun or flash) and your subject. This diffuses harsh light, making it softer and filling some shadows. The translucent panel can also be used to reflect some light, and of course you could combine panels for added effects. Beyond reflecting and diffusing light, any of the surfaces could be used as a background in a pinch, especially the black and white panels. I'm sure with a little creativity one could find dozens more uses. I hope this helps!
Thank you so much John, this was helpful. One more question, will this reflector "fit" on a Sony a900?