For those not familiar with the concept, a white box is a structure used to diffuse light within a certain space. Specifically, it uses light-colored surfaces to reflect, and amplify, the light emanating from one or many light sources. Its uses are more technical than artistic, when showing an object in the clearest, most realistic and most detailed fashion is more important than any creative composition.
White boxes come in various sizes and designs, depending on what is being photographed; if you’re running a low-light setup, I’d recommend being minimalistic when it comes to the size of your box if you want to get the most out of it. It is also recommended that you choose a light source that emulates natural lighting, so as to preserve the accurate colors of whatever it is you are photographing. White boxes can generally be bought, but you can also get creative and build one yourself with things you already have if you want to save a few dollars, or just have fun. Mine, for example, is made of styrofoam and cardboard: