A portable reflector is simply an item that reflects light onto a object, but is compact enough to take anywhere. They are very useful in photography because you can easily manipulate your subject. An example of a use would be when shooting portraits outside. You may often see hard shadows across the face, under the chin, but with the reflector you can reflect light onto these areas and instantly improve an image. You will find they often come in a circle or square shape and there are many sizes for different styles of photography. For example, large objects such as cars need a bigger reflector than a plant. Get as close to the subject/person as you can without being in the shot. Its often a good idea to get a friend or co-worker to help hold the reflector or, you can attach them onto a tripod. Aim for an even glow across the subject without any shadows. And pick the right reflector for the situation, think about the available light.